Talk:Ellipse/Archive 2

Archive 1

Archive 2

General polar form

The section General polar form gives without citation a general formula. See this math reference desk discussion of 1 Oct. 2012 about whether the formula could be correct. In particular, it seems to me that the radical should have a plus minus sign before it. Otherwise, when the origin is outside the ellipse and the angle theta is such that the ray cuts through the ellipse twice (entering and exiting), the formula fails to give two solutions. Duoduoduo (talk) 15:16, 1 October 2012 (UTC)

Ellipse as Conic Section

Several pages on Wikipedia including this page and the page Conic Sections claim that ellipses are one type of conic section. My idea of such a conic section would result in a curve like an ellipse but with one end with a smaller radius, or 'pointier' than the other. This is backed up by an edit in this talk pages archives which suggests that an ellipse being a conic section is fallacious and the true conic section would be an egg-shape. If this is true, could this be clarified? Otherwise, am I (and the commenter in the archives) just wrong? 124.177.190.63 (talk) 12:57, 19 November 2012 (UTC)

We could sit down and figure out how wide an actual conic section is at chosen points along its length. If we did, we'd find it was symmetrical, like the ellipse it is. Tim Zukas (talk) 19:50, 19 November 2012 (UTC)

Turns out if we choose an example conic section it's easy to show it's symmetricral.

On graph paper draw the line y = x and the line y = -x; the two lines above the x-axis are a cross-section of a cone with its vertex at the origin and its axis along the y-axis.

Draw a line from (-1,1) to (2,2). That's the cross-section of the plane that's perpendicular to the paper and sections the cone. Equation of that line is y = (x + 4)/3.

Call the width of the conic section w (measured perpendicular to the paper). Then (w/2)² = y² - x²  ; substitute (x +4)/3 for y and we find that (as a function of x) w² is an upside-down parabola, symmetrical about x = 1/2 as it should be. Tim Zukas (talk) 02:46, 21 November 2012 (UTC)

Being Ben BernankGrinch of the Federal Reserve stole yet another Christmas from me, I had time to improve upon the Blankenhorn-Ramanujan ellipse circumference formula. This formula provides exact end-points and with a maximum relative error of several magnitudes better than the Ramanujan formula. Some day, the Wiki editors will recognize the improvement, but I am not holding my breath for it.

C~pi(a+b)*(1+3h/(10+sqrt(4-3h)) +(1.5*h^6-0.5*h^12)/((11pi/(44-14pi))+24100(1-h)))

Where a and b are the half length axes and h = (a-b)^2/(a+b)^2

Referencing http://i39.photobucket.com/albums/e191/toomers/ell1.jpg, replace the h^5.20114 with 1.5*h^6-0.5*h^12, and the 19176 with 24100.

See: http://ellipse-circumference.blogspot.com

BEING THIS IS FACTUAL, as anyone can check out and I can provide a spreadsheet to anyone interested this should be able to be showing on wiki's site for people to have easy access to. When there is no doubt about the veracity, there should not be power mongers preventing publication. Numbertruth (talk) 00:41, 26 December 2012 (UTC)

It would be nice for the general public to see an equivalent form of the Ramanujan II formula without the Hoelder mean:

C~pi(a+b)[1+((x-1)^2(10(x+1)-sqrt(x^2+14x+1)))/((x+1)(33x^2+62x+33))], where x=b/a

Anyone here should be able to verify this. If the power structure here still doesn't want this shown to the public, well, I made my appeal.Numbertruth (talk) 08:41, 9 January 2013 (UTC)

an approximation to an ellipse with a circle

I simply didn't understand what exactly was meant here. Is the approximate ellipse which is really a circle is to be drawn with 2 compasses or with one? Perhaps a picture, or more precise details, or a reference would resolve the lack of understanding. — Preceding unsigned comment added by 31.44.140.246 (talk) 19:29, 19 December 2012 (UTC)

Reason for reverting edit

I'm reverting the formula added today for the circumference, because the only citation given is http://ellipse-circumference3.blogspot.com/ , which is not a WP:reliable source according to Wikipedia standards. And that blog itself gives no other reference. Wikipedia requires that the formula be sourced to a refereed publication. Duoduoduo (talk) 20:53, 2 October 2012 (UTC) Actually MrOllie beat me to it! Duoduoduo (talk) 20:55, 2 October 2012 (UTC)

A formula of such a great breakthrough does not require a reference other than the formula as standing on its own. Show me one simplistic, one step formula capable of producing 8 significant digits, without the use of the Hoelder mean, and without using pi. Why reference a site that is not used as a blog as a blog? Was there any blogging on it? No! So why was the word "blog" mentioned"? If a person had a site named "mountainspot" would it really trip a person up if it wasn't about mountains? Get past the needless block and inspect the formula to see the tremendous contribution. If a person suddenly came up with an explicit formula, I suppose there will be haters of the contribution for wanting some encyclopedia to first publish it. Amazing. Please ask a mathematician about this - one who is versed in it, such as Michon or Cantrell. This amazing formula needs to be out in the open to be shared throughout the world to simulate investigation of the form used. Note that the error function listed on the site verifies the quality.Numbertruth (talk) 03:45, 3 October 2012 (UTC)

No, even a formula for a 'great breakthrough' requires a source that meets wikipedia's guidelines. This reference is a self published site, so it does not qualify. Since this is a very important formula, no doubt the mathematics community will notice it quite rapidly and write about it in a few peer reviewed journals, we can afford to wait until then. - MrOllie (talk) 10:57, 3 October 2012 (UTC)

Well, so it is, but some things just won't make it into journals when the one coming up with the material is not part of the status quo.

Look at these three new forms I derived using the artithmetic-geometric mean:

http://mathforum.org/kb/thread.jspa?threadID=2422080&messageID=7942499#7942499 C = 4*(pi*(e-1)*e*(e+1)*(d/dx)[agm(1,(1-x=e)/(1+x=e))]-pi*(e-1)*agm(1,(1-e)/(1+e)))/(2*(e+1)*agm(1,(1-e)/(1+e))^2)

http://mathforum.org/kb/thread.jspa?threadID=2420827&messageID=7937451#7937451 C=8e^2(1-e^2)*d/dk(K(k=e^2))+2(1-e^2)*pi/(AGM(1,sqrt(1-e^2)))

http://mathforum.org/kb/thread.jspa?threadID=2428401&messageID=8048879#8048879 C = 4*E((1-x)^2/(1+x)^2)= (2pi)*((((d/dx)[AGM(x,x^2)]|x=Q)*(1-x)*x^2)/agm(x,x^2)^2 + (2x^2-x)/agm(x,x^2))

Where Q = (1-e)/(1+e) = (1-sqrt(1-b^2))/(1-sqrt(1-b^2)); e= eccentricity, and b = length of minor axis.

These formulas make it easy for anyone to compute the ellipse circumference since the agm is simplistic and converges rapidly, thus so little effort would be required. The derivatives of the agm function require a good numeric processor, but other than that, these add to the theory on ellipses. As can be noticed, since I am not of the group that wants to reward those with credentials, progress will be slow. I saw this even when I was inventing in the sciences - it simply produced jealousies and then I get shut out. I hope this changes as humans need to look beyond certification to assess quality.

I will wait, even if I am long gone as this is what may happen.

I have noticed errors and some parts needing clarification regarding elliptical integrals on wiki but I'll leave it to the experts to spot.  :) You may delete the earlier discussion regarding the pade variant or if you give me permission, I will do it. I don't want to do anything here I am not suppose to do. 184.100.17.31 (talk) 07:44, 22 December 2012 (UTC)Numbertruth Numbertruth (talk) 00:27, 11 January 2013 (UTC) A formula I just came up with today is simplistic, having a maximum relative error an entire magnitude lower than Ramanujan's second formula: C~4a[1+(pi/2-1)/(((1-sqrt(2)/2)+(sqrt(2)/2)*(b/a)^(-0.454))^(2pi-2))] Maximum absolute relative error: ~3.8E-5, note: b<>0.

This certainly is noteworthy to be inserted on the main page. Waiting around for this being shown in a popular publication shouldn't be the major point in preventing the world from seeing this. Numbertruth (talk) 05:46, 18 January 2013 (UTC)Numbertruth (talk) 19:35, 19 January 2013 (UTC)

I just edited the circumference section adding Bessel's series (which converges much more rapidly than the series in e). I also removed an elaborate series which is unlikely to be of much practical use. For people who need to compute the circumference accurately for very eccentric ellipses, I included the necessary AGM method (following the paper by Carlson). cffk (talk) 18:25, 10 April 2013 (UTC)

The AGM method is good to have on this site. I went about it in a different fashion in three different forms, referenced above. I still think the direct and quite simplistic formula that has a maximum relative error an entire magnitude lower than Ramanujan's second formula should still get some mention here without first being touted by third-party "experts" since most anyone at the middle school level would be able to verify this and make the appropriate comparison: C~4a[1+(pi/2-1)/(((1-sqrt(2)/2)+(sqrt(2)/2)*(b/a)^(-0.454))^(2pi-2))] Maximum absolute relative error: ~3.8E-5, note: b<>0. Find a formula better than this that has just one number that isn't reduced into a simplified form (even the "0.454" could be altered to "5/11"), without converting a and b into some other number such as the Hoelder mean, and having this low of a maximum absolute relative error. Fellow Mathematicians, I am calling upon you! You may see the formula in normal format at http://ellipsesummary.blogspot.com/ I further contend that Zafary's formula deserves mention here as it's such a neat formula.Numbertruth (talk) 04:15, 4 June 2013 (UTC)

In comparison with Ramanujan's formula that is shown on the main page versus the formula shown immediately above, the relative errors are (when a=1, b varies, with no loss of generality): b Ramanujan II Blankenhorn 0 4.023E-04 --- 0.00000001 4.023E-04 2.220E-16 0.000001 4.023E-04 1.952E-12 0.00001 4.021E-04 1.477E-10 0.0001 3.998E-04 9.635E-09 0.001 3.784E-04 4.750E-07 0.01 2.390E-04 1.206E-05 0.1 1.156E-05 8.321E-06 1 0 0

And so, one must wonder why there needs to be some sort of POPULAR recognition before allowing a very good formula to make it onto wiki? Please explain. This is so simple that just about any low level mathematician could verify.Numbertruth (talk) 17:48, 14 July 2013 (UTC) Since the format is not easily seen for the relative erros shown above, a table form of the results are provided at: http://ellipsesummary.blogspot.com/ And so, the question still remains, why must there be a popularity contest to be able to provide such an advancement for all interested parties to be able to easily view? Again, this is something a low level mathematician could verify, in fact having just low level skills with a spreadsheet program and possessing a middle school math ability, one could easily verify what I am saying without requiring a vote of confidence from the math community.Numbertruth (talk) 17:59, 14 July 2013 (UTC)

Numbertruth, Back in the "old days" when computers were slow and numerical methods less well developed, there was often a need for a "numerical best fit" to a special function. (Some of the approximations for elliptic integrals listed in Abramowitz and Stegun fall into this category.) However I would not be happy with this situation nowadays, particularly in regard to computing the circumference of an ellipse. Why? Because I can't easily access a better approximation of the same type (possibly in conjunction with higher precision arithmetic) to verify that the one I'm using is good enough. So instead I use the Ivory/Bessel series if the eccentricity is small, and the exact formula (evaluating the elliptic integral via the AGM) if the eccentricity is large. In both cases, I have the option of compiling my code with long doubles (and adjusting the convergence criterion accordingly) to verify that the answers I'm getting with double precision are good enough.

So when are other approximate formulas interesting enough to include in Wikipedia? I can think of a few reasons: if it's simple enough for "mental arithmetic" ($\pi (a+b)$ falls into this category); if it's already in wide use or is of historic interest; if deriving the approximation was itself interesting; if your name is Ramanujan (because it's quite likely that the previous reason applies too). Your approximations don't fall into any of these categories. If Wikipedia includes yours, then soon there's be a whole family of variously elaborate formulas. And I can't envision any situation where I would prefer to use formulas of this type. cffk (talk) 20:38, 14 July 2013 (UTC)

P.S. You might be able to interest Paul Bourke in including your result at Circumference of an Ellipse. cffk (talk) 22:12, 14 July 2013 (UTC)

Numerical and linear eccentricity

Unfortunately, nowadays there is a confusion in notation. Traditionally the linear eccentricity should be denoted with the latin e, and the numerical eccentricity should be denoted with the greek ε, where e=εa. Even on this page there is an obvious confusion in notation.Theodore Yoda (talk) 15:29, 25 March 2013 (UTC)

Polar angle

Parametric form in canonical position, missing angles in drawing

I agree with the archived comment requesting labels on the diagramme http://en.wikipedia.org/wiki/File:Parametric_ellipse.gif. —DIV (138.194.10.62 (talk) 06:54, 12 May 2013 (UTC))

Accuracy of formula

Mathworld seems to have a different formula as their #58 compared to Ellipse#Parametric_form_in_canonical_position. I think WP is correct, but am puzzled at the discrepancy. —DIV (138.194.10.62 (talk) 06:55, 12 May 2013 (UTC))

Etymology

Quoth The name ἔλλειψις was given by Apollonius of Perga in his Conics, emphasizing the connection of the curve with "application of areas".

I don't get this sentence. Is an ellipse called so because it's a defective circle?

Thanks, Maikel (talk) 09:48, 27 May 2013 (UTC)

Open and unbounded curves

Currently the lede says

Ellipses have many similarities with the other two forms of conic sections: the (open curve) parabolas and the (unbounded curve) hyperbolas.

This implies that parabolas are open but not unbounded, while hyperbolas are unbounded but not open. But it seems to me that both are open and both are unbounded -- if so, I think this needs to be reworded. Duoduoduo (talk) 21:09, 19 July 2013 (UTC)

I edited that sentence from what it was previously just today. The difference between unbounded and open did not make sense to me. I was merely trying to keep what seemed to be there already. My thought process was that maybe mathematicians made a distinction between the two. I would hate to think that I introduced an error by misinterpreting what was previously there. Perhaps it would help if someone can look at what was there before I edited it. TStein (talk) 05:39, 20 July 2013 (UTC)

Simple proof of the area formula

Duoduoduo: My proof that you just reverted was probably much more useful that the one that you replaced it by, since it used a "known" result (the area of a circle) and a simple geometric argument that anyone who's mathematically inclined could follow. Jacobians and integration seem like complete overkill. However, I don't care enough to press the case. cffk (talk) 21:11, 21 July 2013 (UTC)

The "unproven" and "intuitive" result is proved as follows: the area $A$ is given by the integral

${\begin{aligned}A&=\int _{-a}^{a}2b{\sqrt {1-x^{2}/a^{2}}}\,dx\\&={\frac {b}{a}}\int _{-a}^{a}2{\sqrt {a^{2}-x^{2}}}\,dx.\end{aligned}}$

The second integral is just the area of a circle of radius $a$, i.e., $\pi a^{2}$; thus we have $A=\pi ab$. In my book, this proof is so straight-forward that it doesn't need to be spelled out (and certainly the ancient Greeks found these results without resorting to calculus). cffk (talk) 00:11, 22 July 2013 (UTC)

Uncited and dubious approximation formula

I have marked an uncited approximation formula as dubious. The article claimed it was 'better' but some simple comparisons with (1) Gnuplot's numerical elliptic integral routines, and (2) the Ramanujan approximation formula given in the article showed that the Ramanujan formula was always a better choice. I tested with a and b close to 1, close to 100, and various relative magnitudes of |a/b|.

It is possible that my little tests were somehow biased. I am not in a position to become more familiar with the various approximation schemes and cannot suggest a better formula. Frankly, the Ramanujan formula was a very good approximation. — Preceding unsigned comment added by 69.172.168.8 (talk) 04:04, 31 July 2014 (UTC)

I added back the 2nd Ramanujan approximation as someone compared it with his first in the Circumference article and the results were noticeably better as b got smaller (the other equation for a "special case" is another story-I don't know what the purpose of that was!).2001:4BA0:FFF4:10B:0:0:0:2 (talk) 18:09, 15 September 2014 (UTC)

Fair enough. But the way to make this "stick" is to include the reference to Ramanujan together with his error estimates. I've now added these. cffk (talk) 18:57, 15 September 2014 (UTC)

Circumference

This is going nowhere and this is not the correct place for this. The correct approach has been explained repeatedly, far more times already than is necessary.
The following discussion has been closed. Please do not modify it.
anyone who knows how to calculate area knows how to change the shape of a two dimensional object while keeping the same area I have proposed several times that these laws of geometry as I call them apply to calculating the circumference of an ellipse that by adding the x and y radii you will end up with the diameter of a circle with equal area as the ellipse as well as an equal perimeter who ever is calculating the circumference with these awful equations needs to realize there are 360 degree's in an ellipse no mater how you tweak it as long as the right and left half are mirror images this equation works so please check your math and make sure it works on a circle as well as an ellipse because your equation should cover a broad area and not focus on something we all learned in 3rd grade, that there is 360 degrees in a circle regardless of the dimensions.68.185.82.178 (talk) 02:24, 6 November 2014 (UTC) I calculated the area of a Ellipse (x-axis/2)(y-axis/2) 3.14= here is my equation (6/2)(3/2)3.14=14.14cm then I calculated the size of a circle with equal area using this equation √(6/2*3/2)^2 the problem I found is that the circumference of the circle with a diameter of 4.5cm is equal to the area of the ellipse but the area of the circle is not equal to the area of the ellipse. This is inconclusive because the areas should have been equal but instead the circumference was equal to the area. I need a further explanation because I'm sure my math was right so I think one of these equations are wrong (3.14 x r^2 = area for a circle) (x-axis/2)(y-axis/2) 3.14 = area of ellipse/oval 68.185.82.178 (talk) 02:33, 24 November 2014 (UTC) The original poster is wrong. There is no simple closed-form for the arc length of an ellipse in general. The best you can get is an elliptic integral in most cases. In fact it is true in general that same areas → same circumference is false. Take rectangles and squares for example.--Jasper Deng (talk) 03:32, 24 November 2014 (UTC) rectangles and square have, "perimeters" a 4 by 2 rectangle has the same perimeter as a 3 by 3 square and the same area is ""true"" so what I'm trying to say is an ellipse is just an elongated circle and a circle can have the same area as a ellipse witch will also have the same circumference. Read the article on ellipse it clearly states the correlation of a circles and ellipse.68.185.82.178 (talk) 03:47, 24 November 2014 (UTC) That is complete nonsense. It is a well-known fact that any circle has the shortest circumference of all possible ellipses with the same area. A 4 by 2 rectangle has area 8 and a 3 by 3 square has area 9, which in fact is yet another counterexample to this notion. If you're still not convinced, try using the arc length formula ${\text{Circumference}}=\int _{0}^{2\pi }{\sqrt {b^{2}\sin ^{2}(\theta )+a^{2}\cos ^{2}(\theta )}}\ d\theta$. If a = b then the integral is trivial. One clearly sees that the results could not possibly be equal. If you differentiate under the integral with respect to either a or b, clearly the result depends on both a and b, which contradicts your notion that it is invariant under a scaling of a and b. The same story applies to area. The only way your notion could possibly be true is in a non-Euclidean geometry of some sort but that's not what the article is concerned with. --Jasper Deng (talk) 03:56, 24 November 2014 (UTC) okay true a 3 by 3 has an area of 9 and a 4 by 2 has an area of 8 but the perimeter's are the same 12 but that is not what I'm trying to say its totally of topic I'm referring to the circumference of an ellipse equal to the x+y radii multiplied by Pi 3.14 by adding the x and y radii you are averaging out the ellipse to the proportion of a circle the perimeter is the same as the circumference I was not thinking about rectangles and was trying to find why the area changed or was off.68.185.82.178 (talk) 04:06, 24 November 2014 (UTC) No, just no. Please apply the actual formulas (if you can't do integral calculus yet I'd suggest avoiding this particular topic for now). You cannot just wave your hands and say "I'm 'averaging out' the ellipse". It doesn't work that way. I already gave the correct formula yet you continue to insist on a blatantly incorrect one. The burden is on you to justify how that equation of yours agrees with the arc length formula, which it obviously doesn't. Intuition is useful but never enough to prove something.--Jasper Deng (talk) 04:10, 24 November 2014 (UTC) okay I'll wave my hands and say "I'm 'averaging out' I have no idea how to understand your formula if it had actual information "numbers" I could figure it out it's not really above my head but I do need actual information my major is computer science and this is the information age.68.185.82.178 (talk) 04:17, 24 November 2014 (UTC) Then I can't really help you. This is a very basic math principle that applies in computer science too: all theorems and results must be justifiable by rigorous proof. If you're not willing to embrace that, then I can't direct you to the correct answer. You do not need numbers to analyze the formula symbolically. Numerical integration would be besides the point here anyways. Try the problem of minimizing $C=\int _{0}^{2\pi }{\sqrt {b^{2}\sin ^{2}(\theta )+a^{2}\cos ^{2}(\theta )}}\ d\theta$ subject to the constraint $A=\pi ab$ for constant A. It is very easy to show with differential calculus that a = b provides the smallest circumference for a given A and therefore your notion cannot possibly be correct. If you need help with that you can ask at WP:RDMA, however all the way you have to be strict with what you do. So far I see nothing concrete with your assertion.--Jasper Deng (talk) 04:26, 24 November 2014 (UTC) You need to learn to make everything you say well-defined. There's no room for ambiguity here.--Jasper Deng (talk) 04:26, 24 November 2014 (UTC) "It is a well-known fact that any circle has the shortest circumference of all possible ellipses with the same area" We just 'proved' this wrong with the rectangles that circumference is not equal to area to shapes can have an equal circumference but they don't have to have the same "area" and I would really like to see you do some differential calculus that was a good Idea I'll probably try that.68.185.82.178 (talk) 04:40, 24 November 2014 (UTC) The burden is on you to prove your formula so I will leave the differential calculus to you (hint: $\int _{0}^{2\pi }\cos ^{2}(\theta )-\sin ^{2}(\theta )\ d\theta =0$). If you claim $C=\pi (a+b)$ then you will have to show that it agrees with the integral form. But this is not possible. It has already been shown that the elliptic integrals have no closed form solution and this would contradict that. This is also not possible because the ellipse necessarily has a circumference longer than C=\pi(a+b). If we expand the binomial expansion of the integrand of the arc length formula for a/b almost 0 (an extreme case, but your formula has to hold for all ellipses if you want it to be true), $C=2\int _{0}^{\pi }b\sin(\theta )(1+{\frac {1}{2}}({\frac {a}{b}}\cot(\theta ))^{2}\ ...)\ d\theta$ (we must take only half the ellipse because sine is an odd function and would have had to be put under an absolute value sign if we used the whole ellipse) and select the very first term, $C\approx 2\int _{0}^{\pi }b\sin(\theta )d\theta =4b$. Since all the other terms are only positive they only contribute positively to this result, meaning this result is a lower bound on the circumference. But this is clearly greater than $\pi (a+b)\approx \pi (b)$ (remember a is much smaller than b e.g. a = 1, b = 10000).--Jasper Deng (talk) 05:22, 24 November 2014 (UTC) Okay I got it your argument makes no sense you can reverse an area equation and find the circumference but the equation to find the area of an ellipse cant be reversed and here is where your argument falls apart because area is directly related to the circumference I thought about the rectangle and square idea you had but it to was wrong a 2 by 4 rectangle has the same area as a 2 by 2 by 3 by 3 shape "3 by 3 missing a corner" 68.185.82.178 (talk) 00:11, 25 November 2014 (UTC) Further more I'm directly referring to the relation between the area and circumference its easy to manipulating the perimeter of a rectangle and I'm not manipulating the circumference of the ellipse or the circle I'm calculating the area in relation to the size and shape and assuming the volume remains constant the shape can change but the area remains the same68.185.82.178 (talk) 00:33, 25 November 2014 (UTC) No. Circumference and area in general are not related. And "a 2 by 4 rectangle has the same area as a 2 by 2 by 3 by 3 shape '3 by 3 missing a corner' " makes no sense (everything you said in that phrase beyond the rectangle is ill-defined). I just gave you a concrete calculation that completely debunked your so-called formula. Yet you continue to have this wrong notion. Now you're conflating volume into this? Area is not directly proportional to circumference in the general case. It is only directly proportional to circumference when the coordinates are transformed only by multiplication by the same scale factor. In other words, for ellipses, the relation of C being proportional to area and vice versa is only valid for when a and b have the same ratio. I also clearly demonstrated that constant area does not lead to constant perimeter/circumference. What does volume even have to do with this? I suggest you build a proper background in this area first. You can't have a discussion like this if you're going to make everything ill-defined, vague. I also would appreciate it if you would not type with run-on sentences. Thank you.--Jasper Deng (talk) 02:04, 25 November 2014 (UTC)

Removed images

I removed the image of Saturn as it is only an interesting tid bit, if you can even call it that. It is completely irrelevant to the actual article. I also removed the image of the conic section. I do not know what type of shape a conic section is classified as but i know it is not an ellipse. An ellipse is obtained by taking a cross section of a cylinder. (Angled cross section if you want a non-circular ellipse) — Preceding unsigned comment added by 173.166.173.129 (talk) 16:39, 3 March 2015 (UTC)

Once again removed the image that attempts to show am ellipse as a conic section. — Preceding unsigned comment added by Dubsed (talk • contribs) 05:18, 6 March 2015 (UTC)

Please stop removing this image. It is correct and ellipses are conic sections. It is true that you get ellipses as cross sections of cylinders, but this is because a cylinder is a special type of cone, namely a cone with vertex at infinity. One should not use this special case as the defining instance for the ellipse, especially when all the conic sections can be obtained from a more general cone. Bill Cherowitzo (talk) 16:43, 6 March 2015 (UTC)

My apologies. I stand corrected. — Preceding unsigned comment added by 173.166.173.129 (talk) 12:54, 9 March 2015 (UTC)

Mixed case in variables

Although I am a moderately good mathematician (MSEE) I may be missing something, but short of that it seems to me that the mixed case for the variables in this article is unconventional and misleading. Unless I hear otherwise, at some point I am going to clean it up. For one thing is looks sloppy and makes the article harder to read, but more than that novices to the subject should not have to wonder if there is some special implied meaning for $X$ versus $x$. LaurentianShield (talk) 15:32, 30 August 2015 (UTC)

And BTW I am not talking about usages of all capital letters, but primarily the mixed $X$ versus $x$ and $Y$ versus $y$. LaurentianShield (talk) 15:36, 30 August 2015 (UTC)

I agree. Especially beginning with the section, In analytic geometry, the upper case X and Y should be lower case. If you would like to clean this up, then I encourage you to do so. Thank you! — Anita5192 (talk) 16:05, 30 August 2015 (UTC)

Fundamental prove missing

In the "equations" part appears: "Then plotting x and y values for all angles of θ between 0 and 2π results in an ellipse (e.g. at θ = 0, x = a, y = 0 and at θ = π/2, y = b, x = 0)." It should be proven, it also speaks about a certain $\theta$ angle which should be defined — Preceding unsigned comment added by 88.13.77.209 (talk) 14:37, 20 July 2015 (UTC)

The proof was, and is, already in there, immediately after that sentence. I'll clarify the transition from the statement to the proof, and I'll put in a definition for theta. Loraof (talk) 15:24, 19 November 2015 (UTC)

Wrong formula?

The following subsection was put in on 4 May 2009 by an editor with no other math edits:

==== Polar form relative to center ====

Polar coordinates centered at the center.

In polar coordinates, with the origin at the center of the ellipse and with the angular coordinate $\theta$ measured from the major axis, the ellipse's equation is

$r(\theta )={\frac {ab}{\sqrt {(b\cos \theta )^{2}+(a\sin \theta )^{2}}}}$

While this seems to be right at theta = 0 and theta = pi/2, I don't think it is correct in general. I believe the correct formula is

$r(\theta )={\sqrt {a^{2}\cos ^{2}\theta +b^{2}\sin ^{2}\theta }}.$

Am I just misinterpreting something here? I'm going to change this unless someone sets me straight. Loraof (talk) 00:44, 20 November 2015 (UTC)

Indeed, I was misinterpreting where the angles were measured from. I've put in a source. Loraof (talk) 02:58, 21 November 2015 (UTC)

News article to consider for inclusion

Baker, Chris (27 Nov 2015). "Elliptical Pool". Wired. Retrieved 29 Nov 2015. --User:Ceyockey (talk to me) 16:40, 29 November 2015 (UTC)

Barycentre

Surely (except perhaps in the case of Jupiter) it is spurious accuracy to refer to the barycentre of the planet and the Sun (rather than just the Sun) while ignoring the masses of the other planets?----Ehrenkater (talk) 14:53, 11 December 2015 (UTC)

Eccentricity

The article says: 'For an ellipse the eccentricity is between 0 and 1 (0 < e < 1)'. Shouldn't this be '(0 ≤ e <1)'? A circle is still an ellipse right? Bgst (talk) 11:25, 11 June 2016 (UTC)

This depends on what one is using for the definition of eccentricity. The formal definition (as given in the Conic section article) involves the distance from the focus to the directrix, and a circle does not have a directrix in the plane, so it doesn't have an eccentricity. On the other hand, the limit of the eccentricity as the ellipse approaches a circle is zero, so many authors would define the eccentricity of a circle as zero. In this article, the eccentricity is given by a formula (⁠f/a⁠) which is a property and not a definition. This formula also gives the eccentricity of a circle as zero (since for a circle f = 0), but this is misleading since it hides the true nature of what is going on. Finally, in the broader context of projective geometry, it makes sense to say that the directrix of a circle is the line at infinity, and with that understanding the eccentricity of a circle can be computed to be zero. So, the answer to your question is both Yes and No, it depends on what assumptions you are making about the context. Many authors leave it as a strict inequality, while others include the zero value (but indicate that it is included by definition). The way this article is structured, it is difficult to include a proper treatment of this issue. --Bill Cherowitzo (talk) 16:22, 11 June 2016 (UTC)

Edits of the Adlaj formula

I agree with all previous editors that that mention of Adlaj and a link in-line is not appropriate. The formula is interesting and probably belongs in the article (although I have not checked the citation). However, the wording as of the last edit I reverted to is better. "Surprisingly" is a definite "says who" flag for one thing. Let's try to reach consensus here and not repeatedly edit-revert-edit. LaurentianShield (talk) 19:02, 16 July 2016 (UTC)

Sorry, I did not mean to say that you were qualified. I meant the editor whom you reverted. "Surprisingly" is a definite yes to anyone who knows that the formula did not appear before 2011. So in reaching a consensus I suggest leaving out people who "have not checked the citation" and who aren't likely to understand it anyhow. So do not rush to agree with anyone who shares your opinion about things irrelevant to the article.2A00:1370:8128:73E:C811:B591:263B:B6C6 (talk) 19:33, 16 July 2016 (UTC)

The PseudoScientist version states the fact that the formula is actually two sequences (the one a lower bound, the other an upper bound) that both converge quadratically to the ellipse circumference. This is better than the Blackburne version. As I stated in my last edit comment, the date of 2011 is relevant because it is surprising that such a simple formula for something as basic as ellipse circumference would be discovered this recently. I did look at the "Notices of the American Mathematical Society" article. The formula in the Wikipedia article is equivalent to the one in the NAMS article. Jrheller1 (talk) 19:42, 16 July 2016 (UTC)

"Surprisingly" needs someone to say this is "surprising" -- an editor can't just claim this. Editors in general can't just claim "authority" and an anonymous editor can't bestow this "qualification". Everything on Wikipedia needs to be verifiable, no editor can claim authority a priori on any subject, even if they are a subject matter expert in the area. As for the in-line reference to the personal page of the author of the formula, this is highly inappropriate self-promotion. As for whether I am "vandalizing", I am merely reverting to the status quo prior to forced edits of this page. I am about to do that again, and I think we should reach on consensus here first. LaurentianShield (talk) 20:02, 16 July 2016 (UTC)

Vandalizing the work of others before talking is not descent. Editors who can argue their position such as Jrheller1 and PseudoScientist among others are certainly an authority. Of course, I would not want to insult you in spite of all your unqualified actions but I do want to tell you that you certainly not an authority and will never be. You demonstrated this by your untactful, to put it mildly, behavior. You seem to talk but you do not seem to listen to any reason. Certainly, promoting yourself here is highly inappropriate. This is not an article on politics so relax and leave the work for people much more qualified than you'll ever be. Personally, I have no ego problems which would preclude me from promoting anyone who deserves to be promoted and I feel badly for you that you will never be promoted by any competent editor. Please stop bringing your own problems into a scientific dispute.2A00:1370:8128:73E:C811:B591:263B:B6C6 (talk) 20:49, 16 July 2016 (UTC)

"Wikipedia is not a ... vehicle for ... showcasing." (Wikipedia:What_Wikipedia_is_not). "Wikipedia articles may include links to web pages outside Wikipedia (external links), but they should not normally be placed in the body of an article." (Wikipedia:External_link) These two policies taken together are why I don't think it is appropriate to include the link to the paper author's personal page. LaurentianShield (talk) 21:02, 16 July 2016 (UTC)

I previously reverted the insertion of the "surprisingly simple and exact formula" because regardless of the journal it was published in, it appeared to be promoting the author who may have been editing under a pseudonym. Reverting it may not have been the right thing to do and I may not have done it in the most graceful manner, but it still looks as if it is original research, promotes the author, is esoteric enough to be hardly relevant, and one editor appeared to be performing the same edits from different accounts. I follow the bold, revert, discuss cycle, so I will not revert it again. In fact, nobody should revert it again until consensus is reached on this talk page. I have checked the citation, but I have not verified that the formula works or that it is surprising or useful. Please discuss. — Anita5192 (talk) 20:39, 16 July 2016 (UTC)

Do we have any secondary sources (that is, sources written by someone other than Adlaj about this? That would help us decide how to properly emphasize the importance. Interested editors should also see the history of Arithmetic–geometric mean where some parallel edits have been made. - MrOllie (talk) 21:28, 16 July 2016 (UTC)

I did a search on "Semjon Adlaj" on JSTOR and came up with zero hits -- no hits on the name as an author nor references to the formula by someone else. That does not mean there aren't any somewhere else of course. LaurentianShield (talk) 21:31, 16 July 2016 (UTC)

I agree with LaurentianShield and Anita5192 and MrOllie that the result can be mentioned and reference, but that puffed-up style of the IP 2A00:'s edit is in appropriate. I think the consensus is to go back to before his edits, or a version without them, not put more about this until we have a consensus way to do so. We should ask for the protection to be lifted if he agrees to talk and hold off edits, or ask for him to be blocked and then lift the protection if he does not. Dicklyon (talk) 22:10, 16 July 2016 (UTC)

What a wonderful suggestion! Have him agree or have him blocked! Do not you seem to agree with others who have the same problems of dissatisfaction with their own lives? And one wonders why do all these people who are quick to agree with each other have so little contribution to any scientific Wikipedia articles. This is supposed to be a scientific dispute, not a mutual ego support group. The qualified editors, who are not among those whom you listed, already told you that the formula was surprising because it did not appear before 2011. It was checked by several qualified editors but again by none of whom you agree with. I dare to presume that you did not check it either and you do not understand it, so please correct me if I am wrong. Why won't you frankly tell us what are you so worried about? What "puffed-up style is in appropriate"? Be specific or stay quite before someone else asks to block you for unconstructive intrusion! 2A00:1370:8128:73E:C811:B591:263B:B6C6 (talk) 22:41, 16 July 2016 (UTC)

Actually personally I think it is an interesting formula, I did review the paper. It just so happens I have done some numerical analysis of elliptic integrals as part of my engineering work, so I do understand it. But that's not really relevant to the discussion here. What we need is someone besides another editor to verify where this formula fits in the history of numerical analysis of elliptic integrals, in order to say it is "surprising". This may come from a text on either elliptic integrals, or numerical analysis, for example. If the anonymous user knows of any please please provide the reference. However aside from that, the external link remains inappropriate in my opinion. LaurentianShield (talk) 23:02, 16 July 2016 (UTC)

The title of the article was "An Eloquent Formula for the Perimeter of an Ellipse". The reviewers at Notices of the American Mathematical Society didn't have a problem with the word "eloquent", so why should any Wikipedia editor have a problem with the words "surprisingly simple"? Jrheller1 (talk) 23:28, 16 July 2016 (UTC)

Well it is splitting hairs a little bit, but the article itself is full of subjective assertions like "ridiculous", the math layout is poor (I thought AMS used Tex?), and it is very self-serving -- so I suspect the level of review is low. In and of itself that's not a big deal I suppose, but coupled with the personal promotion of the author it comes across as "un-encyclopedic". In addition "eloquent" is different than "surprisingly simple" -- but that's where the hair splitting comes in. BTW related but somewhat separately, I just wonder whether the whole discussion of numerical analysis of elliptic integrals belongs somewhere else anyway. It drastically overcomplicates the article on the ellipse, whereas a simple statement that C=E(e) and can't be found analytically, and then a reference to numerical analysis of elliptic integrals (in a separate article), might be better. LaurentianShield (talk) 00:08, 17 July 2016 (UTC)

Or a separate section in the same article, but make it clear that to most people they don't need to "worry their pretty little head" about how the elliptic integral is solved, just that it can't be done analytically. When I was using them a lot years ago, I wished my calculator had a "E(e)" button just like it has a "log" button or a "sin(x)" button. That's basically the level of understanding (IMHO) should go in the ellipse article. LaurentianShield (talk) 00:15, 17 July 2016 (UTC)

I like the current version. The only thing I would possibly change is to remove the last sentence "This concise formula was discovered by Semjon Adlaj on December 16, 2011". Adlaj is apparently not notable enough to be mentioned in the article (as Bessel and Ramunujan are). Jrheller1 (talk) 22:56, 16 July 2016 (UTC)

But it is not surprising, unless sources say so. It is not simple. It looks simple and direct but the two terms M and N are iterative processes, each less amenable to direct calculation than the earlier infinite series. One of these is the 'modified arithmetic geometric mean', not a standard process but one seemingly especially created for this formula. Which also means it is not exact as an exact result would require an infinite number of calculations.--JohnBlackburne^words_deeds 23:22, 16 July 2016 (UTC)

Now the discussion is becoming much more constructive. I also agree that mentioning the author is not necessary, although not mentioning him would not really be consistent with the scientific integrity rules, so let's see what PseudoScientist would have to say here. I also looked into the article and I think that mentioning the exact date is rather important. The fact that no such "concise" formula was available before 2011 is most certainly surprising. We might suggest another word other than "concise" but on the other hand there isn't any problem with it, is there? So, in brief, I side with Jrheller1. Removing the author's name from the text is acceptable and changing the wording is possible provided the date stays. Otherwise, the word surprising would not be correctly interpreted. I also side with Jrheller1, who emphasized the advantage of the current formulation which emphasizes both upper and lower bounds. 2A00:1370:8128:73E:C811:B591:263B:B6C6 (talk) 23:39, 16 July 2016 (UTC)

I strongly disagree with removing the author's name from the text. That would simply be dishonest and no such rules could have possibly been invented by wkipedia or whoever else since such rules would then and indeed contradict "the scientific integrity rules", as was already suspected. I see no reason to satisfy the editors who do not want to see author's name, of the formula being discussed, given in the text. I bet they would not mind having their names instead although they certainly do not deserve that. I do not mean the anonymous editor and Jrheller1 who do not have the problems that other less competent editors do. However, they seem to yield this issue to other editors who unlike them do not quite understand the significance of the formula, as evident by incessantly confusing it with power series formulas and saying that it is not exact and other incompetencies. Even more, I think that both mentioning the author and providing a link to his web site are appropriate. In fact, there is sufficient material about him to initiate a wikipedia article about him and I would not be as certain to say that his contributions are less significant than Ramanujan's. But that is just my personal opinion, based on researching his articles. PseudoScientist (talk) 00:16, 17 July 2016 (UTC)

I am being subjective when I say this, but I definitely would not compare Semjon Adlaj with Srinivasa Ramanujan -- that would be an enormous disservice to Ramanujan! I can only find one article by Adlaj BTW (the one in question). Can you list any others? LaurentianShield (talk) 00:28, 17 July 2016 (UTC)

I suggest you go to his web page that you have been so keen getting rid of from the article and you can find many more materials on the issues which you repeatedly and unsuccessfully tried to address in this ongoing discussion. I must warn you though. Plenty of original research which you would not be able to assess. Good luck. PseudoScientist (talk) 00:38, 17 July 2016 (UTC)

Thanks! I checked -- eight papers. Only some of them are peer reviewed Semjon Adlaj. They are not completely insignificant, but hardly Ramanujan -- which was my main point. I suspect a Wikipedia article on Adlaj would not last long from the perspective of notability. LaurentianShield (talk) 00:57, 17 July 2016 (UTC)

What about changing the words "A surprisingly simple and exact formula" to "A much more efficient formula"? Jrheller1 (talk) 01:51, 17 July 2016 (UTC)

I would go along with that. LaurentianShield (talk) 02:07, 17 July 2016 (UTC)

But it s not much more efficient, unless you have a source saying so. My own intuition is that it is less efficient than e.g. the rapidly converging series immediately above. --JohnBlackburne^words_deeds 02:08, 17 July 2016 (UTC)

Some of that hinges on how well peer-reviewed the paper is. The paper claims it is more efficient than any other algorithm. On the other hand, the paper is not real clear on any sort of proof, it merely makes the claim and then gives examples. I hate to sound wishy-washy :) I definitely wish ther was some other reference to the paper. So far I am drawing a blank. LaurentianShield (talk) 02:14, 17 July 2016 (UTC)

The paper was reviewed by Math Reviews (MR 2985810). The reviewer (Davide Batic) did not express surprise, mention eloquence or efficiency. He simply stated that the author had found a concise formula. It should be noted that the Notices, being a magazine, may not vet its math articles in the same way that other AMS publications are refereed. I could not find any evidence that this paper had been cited by any other authors, but there is always a time lag in these things so I would not give that much weight. --Bill Cherowitzo (talk) 04:16, 17 July 2016 (UTC)

Do you have a link please? I can't find the Baltic review. It would really help settle the remaining issue over wording. LaurentianShield (talk) 17:24, 17 July 2016 (UTC)

@LaurentianShield: It's MR2985810, but you need MathSciNet access to read it. In the usual style of MathSciNet, it's just a dry and factual statement of the results of the paper, without the sort of editorialization we're arguing about here. Its entire text is:

"The values of complete elliptic integrals of the first and the second kind are expressible by means of power series representations of a hypergeometric function. It is known that the complete elliptic integral of the first kind can be expressed in terms of an arithmetic-geometric mean, whereas a similar formulation for the complete elliptic integral of the second kind has been missing. The author succeeds in deriving a concise formula that gives rise to an exact iterative swiftly convergent method which makes it possible to compute the perimeter of an ellipse."

—David Eppstein (talk) 17:38, 17 July 2016 (UTC)

I think it's safe to assume that NAMS would have verified that the formula is actually correct, although there may be a very small chance they did not. As far as the efficiency goes, it is not very difficult to check this. For a=2, b=1, computing in double precision, the Ivory-Bessel series requires 23 terms to reach machine epsilon of approximately 1e-16 (the 22nd term is above machine epsilon, the 23rd term is below machine epsilon). Both MAGM and AGM only require 4 iterations to get below machine epsilon difference between the upper and lower bound, for a total of 8 square root operations. I have compared the speed of trig operations and square roots on my computer: a cosine operation takes approximately 6 times longer than a square root. Computing a cosine to machine precision requires summing only 10 terms of the Taylor series (up to the term with coefficient 1/20!, which is less than machine epsilon). So this indicates that evaluating the Ivory-Bessel series would take approximately the same time as computing 14 square roots.

So in double precision, the iterative algorithm would be slightly more efficient than Ivory-Bessel (8 square roots + some multiplications and additions versus 14 square roots). But for quad precision (which some applications need), the iterative algorithm would be much more efficient. It would only take one more iteration to get to a precision of 1e-32, whereas the Ivory-Bessel series would take 54 terms to get to this same precision.

So maybe "A formula that is more efficient for high-precision calculations" would be better wording. Jrheller1 (talk) 06:17, 17 July 2016 (UTC)

But a source is needed for that. It can’t be based on your calculations, both as someone with different assumptions might come to a different answer (what if you have hardware that calculates cos, sin and sqrt as fast as multiplication and division?) and more importantly unless a source says it is more efficient then it should not be in the article. If no source thinks it is important to mention its improved efficiency then it’s not a claim we can make.--JohnBlackburne^words_deeds 06:46, 17 July 2016 (UTC)

Well and quite strangely we all seem to be reaching a consensus. Let me summarize. The Adlaj formula is surprising to every mathematician and every physicist but it is not surprising to anyone with primitive knowledge about math and science. So, whoever say that the formula is not surprising are not saying anything about the formula per say but are saying much more about themselves than they seem to realize. Then they wonder how come they were not perceived as competent editors. Certainly, the whole discussion is much more focused on consoling the losers than discussing the formula. To fix that, I suggest starting a new subtitle in the article which would agree with title of this discussion: "The Adlaj formula". There we can include, as well, special values calculated in the said article, where the circumference is expressed in terms of the Gauss constant. Frankly speaking, a competent editor excluding myself but including Jrheller1 and the anonymous editor better email Adlaj directly to inform him of the ongoing discussion. Publishing Adlaj's results on Wikipedia without his permission risks being unethical, especially with all these incompetent editors eager to publish results without due credit. They do not seem to understand that he did not write a paper of the same level of the papers they do. He published his OWN result. As I said, it is dishonest to undermine that. Ramanujan would not but incompetent editors keep on confusing their kevel which his. I am quite certain that Adlaj himself does not care much for publicity which is quite evident by his publishing activity with excludes JSTOR and other public places. I might be guilty pushing his results to wikipedia and that is the reason I suggest contacting Adlaj directly for a permission. I excluded myself since the whole discussion was not started by me and maintaining the ethics is jeopardized with these harmful interventions. I would proceed if no such interventions recur but I would leave the editing to others if they do. But then I would contact him personally to inform him of the improper use of his results by incompetent wikipedia editors in violation of decency rules. PseudoScientist (talk) 07:51, 17 July 2016 (UTC)

I went back (again!) and read the original paper. BTW I also requested above a link to a review of the Adlaj article, which sounds like it will be helpful. In any case, Adlaj merely says "This formula, ... aside from offering a calculating algorithm possessing both iterativity and fast convergence, is lucent." I can't find any claims for how quickly it converges, and it is only compared to one other case not as part of a general assessment. I agree with JohnBlackburne also that the rapidity might depend of special hardware. The issue is pretty esoteric, and really getting outside the realm of helping readers understand ellipses. That's why I made a comment above that I wonder if the whole section should be simplified, and put the algorithms for how the elliptic integral is calculated in a separate section. In any case I am leaning back toward a simple statement of "The circumference can be found using the arithmetic-geometric mean", give the formula, and leave out all adjectives. LaurentianShield (talk) 17:24, 17 July 2016 (UTC)

Both the Ivory-Bessel series and the iterative algorithm are very easy to implement (on a scale of 1 to 10 probably a 1 or 2 and only a few lines of code). So anyone with a basic understanding of numerical analysis and programming could easily check the efficiency, meaning no reference is needed. Considering how simple both the series and iterative algorithm are to implement, I don't consider either one "esoteric". Jrheller1 (talk) 19:25, 17 July 2016 (UTC)

There is one other important aspect of efficiency of the algorithms: efficiency for higher values of eccentricity. For example, for a=10, b=1, the Ivory-Bessel series is very slow: it takes 102 terms for the term to go below double precision machine epsilon. For these same values of a and b, it only takes the iterative algorithm one additional iteration (for a total of 5 iterations) to reduce the difference between the upper and lower bound below double precision machine epsilon. Jrheller1 (talk) 19:25, 17 July 2016 (UTC)

Protected

I have protected this article (in the wrong version) for three days, because of the recent edit warring. Please take advantage of the enforced hiatus on editing to discuss the issue and formulate a concensus rather than merely going back and forth between the two disputed versions. If a consensus does form, please notify me so I can remove the protection earlier. —David Eppstein (talk) 20:24, 16 July 2016 (UTC)

I have asked for sock-puppet investigation of PseudoScientist and IP and FeelUs: Wikipedia:Sockpuppet_investigations/PseudoScientist. Dicklyon (talk) 04:29, 17 July 2016 (UTC)

I wonder why would a photographer, who knows the least about the formula among least competent editors would intervene in a scientific dispute. One needs not contribute if has nothing constructive to say. Who told Dicklyon that all people who do have a constructive contribution are one and the same person? Keep in mind that arguments count in a scientific dispute not simply the total number of statements produced by everyone. Dicklyon contribution is zero at best or, more likely, is negative. So I cannot even tell who's ideas Dicklyon represent to accuse him of the same, since no ideas have been displayed by him. So, please Dicklyon do us all a favor and leave. Spare us from filtering additional noise. Even your supporters do not care to know your bitter opinion because you expose them. PseudoScientist (talk) 11:33, 17 July 2016 (UTC)

PseudoScientist and J20160628 have now been blocked for confirmed sockpuppetry. So there is no longer a need to consider their position in any consensus (if they actually had a position other than insulting the other participants). But I think Jrheller1 still supported the version with the disputed adverbs? —David Eppstein (talk) 15:21, 17 July 2016 (UTC)

I would change the words "A surprisingly simple and exact formula" to "A formula that is more efficient for high-precision calculations", get rid of the last sentence "This concise formula was discovered by Semjon Adlaj on December 16, 2011", and keep everything else the same. Jrheller1 (talk) 17:16, 17 July 2016 (UTC)

That sounds like a step in a good direction, and we could resume normal edits and quibbles from there, if any. Dicklyon (talk) 17:37, 17 July 2016 (UTC)

I can go along with that, particularly in light of a review of the Adlaj article. Please see the quote above. Mathematician Davide Baltic confirms in the review that "The author succeeds in deriving a concise formula that gives rise to an exact iterative swiftly convergent method ..." which is good enough for me to support Jrheller1's wording. Plus I do want to move on from this :) . What do you say @JohnBlackburne:? LaurentianShield (talk) 19:17, 17 July 2016 (UTC)

We should only include what is in sources, and I don’t see where it says more efficient. It is just one word but it implies this is better than other methods, which the article should not assert if it’s not in the references. "swiftly convergent” or some other wording is enough.--JohnBlackburne^words_deeds 23:45, 17 July 2016 (UTC)

I just looked at the Carlson paper for the first time. The method it describes for evaluating a complete elliptic integral of the second kind (in other words, ellipse circumference) is better than the Adlaj method. Carlson's method does not require MAGM, only AGM. In other words, it is twice as efficient as the Adlaj method because it only requires one square root per iteration. So now I am in favor of completely deleting the additions by PseudoScientist. Jrheller1 (talk) 02:41, 18 July 2016 (UTC)

I thought the point of using the MAGM is that it would converge in many fewer iterations. Did I get that wrong (I haven't read it that carefully or compared to the other). Dicklyon (talk) 02:44, 18 July 2016 (UTC)

The Adlaj method requires computing both an MAGM and an AGM and computing their ratio (see the formula in the Wikipedia article). Both AGM and MAGM are quadratically convergent, so they converge in approximately the same number of iterations. Jrheller1 (talk) 02:52, 18 July 2016 (UTC)

OK, let's back it out. Dicklyon (talk) 03:37, 18 July 2016 (UTC)

Unprotected, so go ahead. —David Eppstein (talk) 04:33, 18 July 2016 (UTC)

I backed up to before the IP's latest edit. I'm not sure if that's as far as Jrheller1 is suggesting; I'll let him check. Dicklyon (talk) 04:48, 18 July 2016 (UTC)

I finished removing PseudoScientist's edits and described the B. Carlson method a little bit more thoroughly. Hopefully that resolves this issue. Jrheller1 (talk) 05:51, 18 July 2016 (UTC)

References to an intersection between a cone and a plane should say cylinder & plane

The article states: "In mathematics, an ellipse is a curve in a plane surrounding two focal points such that the sum of the distances to the two focal points is constant for every point on the curve." By that definition every ellipse can be defined by the perimeter of an intersection between a cylinder and a plane, with the semi-minor axis of the ellipse being equal to the cylinder radius and the semi-major axis of the ellipse being equal to the cosine of the angle between the intersecting plane and the circular cross-section (perpendicular to the tube's length).

The article also states: "Ellipses are the closed type of conic section: a plane curve resulting from the intersection of a cone by a plane (see figure to the right)." But the curvature in any plane near the top of a cone is greater than the curvature at the bottom of a cone. Wouldn't the intersection would be egg shaped?

Please have a look at Dandelin spheres.--Ag2gaeh (talk) 16:24, 1 April 2017 (UTC)

The intersection would not be egg-shaped. This can easily be proved algebraically.—Anita5192 (talk) 17:44, 1 April 2017 (UTC)

Intuitively, the plane cuts the cone at a more shallowly grazing angle at the point farthest from the apex of the cone, and at a steeper angle at the point nearest the apex. This exactly counteracts the effect of the cone being less curved farther from the apex and more curved nearer the apex, so that the ellipse ends up being symmetrical. But as Anita5192 says, the easier way to understand this is algebraic — a cone obeys a quadratic equation in 3d, so its intersection with a plane obeys a quadratic equation in 2d. The only non-degenerate curves obeying quadratic equations are ellipses, parabolas, and hyperbolas, so if you get a curve that doesn't go off to infinity you know it must be an ellipse. It is also true that the intersection of a cylinder and a plane is an ellipse, but for historical reasons (the name "conic section") the intersection with the cone has greater significance. —David Eppstein (talk) 21:48, 1 April 2017 (UTC)

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area and circumference

I've been saying this all along the ellipse is just a elongated circle and everyone knows how to find the area and circumference of a circle you have the area equation right now you just need to fix the circumference equation the circumference of an ellipse is a+b/2*3.14 were a and b are the semi-major and semi-minor axes adding them and dividing by 2 gives the average diameter2001:558:6012:1B:5CF8:2FED:C347:768E (talk) 17:56, 26 February 2018 (UTC)

Incorrect. Circumference doesn't scale with elongation like that. See the circumference section of the article for the formula. —David Eppstein (talk) 20:06, 26 February 2018 (UTC)

Polar form relative to center

Let a = 1, and b = cos(β), where β is the angle of tilt, of the minor axis from the z-axis, φ is an angle of rotation of the major axis around the z-axis, angle α =(nθ-φ) is rotation around the z-axis, in a counter clockwise direction.

               r(θ) = 2cos(β)/√(3+cos(2β)(1+cos(α))-cos(α)).

The view of a unit circle becomes more elliptical as it is tilted away from the z-axis, or line of sight.Cuberoottheo (talk) 19:23, 29 April 2018 (UTC)

Not sure what you want to change about the article; otherwise this is off-topic.--Jasper Deng (talk) 19:32, 29 April 2018 (UTC)

Its the articles polar equation, using angles α and β instead of lengths a and b, the number n = 2 for an ellipse, if n = 1 the ellipse is egg shaped, if n ≥ 2 the ellipse has 2 or more major axis .Cuberoottheo (talk) 10:30, 30 April 2018 (UTC)

The unit circle's circumference is 2π radian, tilted its 3√(3+cos(n*β)) radian, viewed area is also reduced to 0.5π(a^2)√(3+cos(n*β))*cos(β).Cuberoottheo (talk) 21:20, 3 May 2018 (UTC)

@Cuberoottheo: This discussion isn't pertinent to the ellipse but, apparently, to some generalization of an ellipse. In addition, your thoughts are evidently still evolving (you've made a dozen or so edits over the past month, with next to no engagement from other editors). I recommend that you move your work to your user sandbox until you're able to articulate some concrete proposals for the article. cffk (talk) 13:39, 10 June 2018 (UTC)

The Normal bisects the angle between the lines to the foci: Section needs editing

This section is either not clear (to me), or incorrect.

The proof included in this section says, "Line w is the bisector of the angle between the lines ..."
The very next sentence says, "In order to prove that w is the tangent line ..."
So is w the bisector or the tangent?
The accompanying graphic on the right indicates w is the tangent, in which case the text should be changed.

The accompanying graphic on the right also includes the statement, "... the tangent bisects the angle between the lines to the foci."

I think it means to say, "... the normal to the tangent at P ...".

David Binner (talk) 19:48, 10 July 2017 (UTC)

A belated thanks for pointing this out. I’ve clarified it. Loraof (talk) 16:40, 12 June 2018 (UTC)

Two circle method to draw ellipse

In engineering drawing class I was taught to draw an ellipse by drawing circles centred on the centre of the ellipse with radii same as the semi axes. One then draws sum diameters and where the diameter intersects the smaller circle draw a line through this parallel to the major axis and similarly the larger one and the minor axis. These meet at a point on the ellipse. This is in textbooks on geometrical and mechanical drawing and I wondered why it does not feature in this article. Billlion (talk) 12:34, 19 March 2019 (UTC)

Because you haven't added it yet! If you do add it, you should include a reference which should be a standard text book (and not some online posting). cffk (talk) 12:41, 19 March 2019 (UTC)

The method was already mentioned in section "parametric representation", but missed in section "Drawing ...". Now I added the method to section "Drawing ..." with some more explanations.--Ag2gaeh (talk) 16:49, 19 March 2019 (UTC)

Bounding Box of General Ellipse

I was looking for some guidance in finding the equations for an axis-aligned bounding box of a general (rotated) ellipse. This clearly involves tangents to extreme points in the plane. That is, the uppermost, lowermost, rightmost and leftmost points. Is there a simple set of relations involving the coefficients of the general ellipse equation? 2600:1700:9C91:2620:B0E9:DDEE:CBD0:F60D (talk) 22:56, 29 May 2019 (UTC)

Incorrect formula in "Canonical form" subsection

The formula for the canonical form coefficients a,b is not correct. I tested it with A=4, B=0, C=1, D=0, E=0, and F=-4, which corresponds to x²/1² + y²/2² = 1, meaning a=1, b=2, but the formula as written gives a=1, b=1/2. Engineer editor (talk) 18:03, 29 May 2019 (UTC)

There was a missing minus sign in the a,b formula. I re-derived the formula from Mathworld (which uses different notations. I guess it should be correct now.64.111.160.24 (talk) 01:42, 12 June 2019 (UTC)

Ellipse: why can't I add a known reference?

Kleuske That page is entirely clear. It contradicts nothing that I have done but you do not seem to understand your own recommendation. And now that your fealth is exposed and after looking up your profile I can tell that you have nothing to do with the editing of the ellipse page. You are in violation of wiki rules trying to conceal someone else, nicknamed Wcherowi who fears to be have his edit warring further exposed. You two seem to be members of some mafia gang parasiting here who will be fleeing elsewhere as soon as they are exposed. What a shame! 83.149.239.125 (talk) 17:04, 25 September 2018 (UTC)

You were bold, Wcherowi, reverted, now you discuss. The discussion has been had before, i understand, but still. Kleuske (talk) 17:09, 25 September 2018 (UTC)

The previous discussion was presumably the one at Talk:Ellipse/Archive 2#Edits of the Adlaj formula? --David Biddulph (talk) 18:06, 25 September 2018 (UTC)

(Edit conflict) My single revert had a very clear edit summary. This reference was the subject of a long discussion on this talk page (now archived, but freely available) that I participated in briefly. The conclusion of that discussion was that there were better techniques available in the literature already and the article was expanded to make these clearer. Adding this reference to that discussion is a clear indication of a lack of understanding of that issue, so I reverted. If you think that this reference supports some statement in the article and would like to see it included, you would have to argue your case here on the talk page and gain some consensus for your view. Your baseless personal attacks against Kleuske and myself are rather childish and unwelcome. They will not help your cause. --Bill Cherowitzo (talk) 18:31, 25 September 2018 (UTC)

Kleuske is wrong again being now more careful with his language. I did not make any bold edits. I just added a single worldwide known reference. Stop imitating a discussion and pretending that the reference was irrelevant. Tell the rest that you are not acting on your own behalf but hiding the shameful reversion of Wcherowi. 83.149.239.125 (talk) 18:46, 25 September 2018 (UTC)

I find the language in Adlaj's paper "With this paper, the quest for a concise formula giving rise to an exact iterative swiftly convergent method permitting the calculation of the perimeter of an ellipse is over!" to be overwrought. The method already cited in the article based on the Carlson symmetric form already satisfies the author's criteria. I recommend leaving the reference to Adlaj out of this article. cffk (talk) 19:12, 25 September 2018 (UTC)

I am sorry to say that the "overwrought language" issue is quite a coward argument against including the Adlaj's formula

$C={\frac {2\pi N(a^{2},b^{2})}{M(a,b)}},$

where $M(x,y)$ and $N(x,y)$ are, respectively, the arithmetic-geometric mean and the modified arithmetic-geometric mean of $x$ and $y$. No one would care much for the words you use as long as you include the formula along with its discussion which must be revived, not hastily archived. So, by the way, according to Adlaj's paper, his formula is based on Gauss' method not Carlson's. In fact, the contribution of Gauss is quite emphasized in the paper but never once was Carlson mentioned. Why would you say that Adlaj's formula is "based on the Carlson symmetric form" without telling us how? And why would you not tell us how Carlson's symmetric form would produce any formula other than Gauss's? How about prohibiting/allowing the mention of Carlson's symmetric form if someone like Bill Cherowitzo (talk) disliked/liked it or disliked/liked the language that Carlson used? 83.149.239.125 (talk) 09:28, 26 September 2018 (UTC)

My expression "method already cited in the article" is perhaps ambiguous. Here "article" refers to this Wikipedia article not Adlaj's paper. I'm not saying that Adlaj's method is based on Carlson.

Let me explain "overwrought". Adlaj's "quest is over" remark leads the reader to assume that he's giving a method significantly better than existing ones. However if I compare python programs for the perimeter of the ellipse based on Carlson's and Adlaj's methods for computing elliptic integrals of the second kind I get

def carlson(a, b):
  """
  Compute the circumference of an ellipse with semi-axes a and b.
  This implements Eqs. (2.36) to (2.39) of Carlson (1995).  Require
  a >= 0 and b >= 0.  Relative accuracy is about 0.5^53.
  """
  import math
  x, y = max(a, b), min(a, b)
  digits = 53; tol = math.sqrt(math.pow(0.5, digits))
  if digits * y < tol * x: return 4 * x
  s = 0; m = 1
  while x - y > tol * y:
    x, y = 0.5 * (x + y), math.sqrt(x * y)
    m *= 2; s += m * math.pow(x - y, 2)
  return math.pi * (math.pow(a + b, 2) - s) / (x + y)

 
def adlaj(a, b):
  """
  Compute the circumference of an ellipse with semi-axes a and b.
  This implements Eq. (2) of Adlaj (2012).  Require a >= 0 and b >= 0.
  """
  import math
  x, y = max(a, b), min(a, b)
  digits = 53; tol = math.sqrt(math.pow(0.5, digits))
  if digits * y < tol * x: return 4 * x
  X, Y, Z = math.pow(x, 2), math.pow(y, 2), 0
  while x - y > tol * y:
    x, y = 0.5 * (x + y), math.sqrt(x * y)
    t = math.sqrt( (X - Z) * (Y - Z) )
    X, Y, Z = 0.5 * (X + Y), Z + t, Z - t
  return 2 * math.pi * (X + Y) / (x + y)

Clearly the two implementation are comparable in terms of conciseness. Concentrating only on the meat of the methods, the while loops, we see that Carlson's method is, in fact, somewhat simpler (one square root instead of two, fewer arithmetic operations). Accepting Adlaj's assertion that the MAGM converges faster than the AGM, the two methods have the same convergences properties (governed by the AGM). This just repeats the analysis done by @Jrheller1: at Talk:Ellipse/Archive_2#Protected on 2106-07-18.

In fact, Adlaj's MAGM has a severe drawback. Even though it converges rapidly, it is numerically ill-conditioned. The iteration for Y involves a subtraction of 2 nearly equal quantities. If the MAGM is stopped when convergence is first reached, this only results in a loss of a few digits of accuracy. But allowing a few more iterations, "just to be on the safe side", results in increasing errors because Z roughly doubles on each iteration. The AGM does not have this defect; with finite precision it quickly converges to a constant state.

Finally, Carlson's 1995 paper gives state-of-the-art methods for computing all the elliptic integrals (complete and incomplete). (Carlson is the author of the chapter on elliptic integrals in the Digital Library of Mathematical Functions.) So it you need to compute a meridian arc (the length of a portion of the ellipse) in addition to the full perimeter, Carlson's paper provides a comprehensive solution.

cffk (talk) 15:25, 26 September 2018 (UTC)

Firstly, I must thank you cffk (talk) for clarifying that "Adlaj's mathod is not based on Carlson's". You have also "clearly" noticed that "the two implementation are comparable in terms of conciseness" and that they "have the same convergences properties (governed by the AGM)" but have you wondered why? I have googled the Modified Arithmetic-Geometric Mean and I have found this link https://math.stackexchange.com/questions/391382/modified-arithmetic-geometric-mean which answers the question. So, the two implementations are not only comparable "in terms of conciseness" but they have EXACTLY the same convergence if EXACT arithmetic is used. Both being implementations of MAGM as said in Adlaj's paper. You and @Jrheller1: seem to have confused the definition of MAGM with the way to calculate it which was also told in Adlaj's paper. You also seem to have confused comparing the relative speed with which AGM and MAGM converge with comparing two methods. There were no two methods in Adlaj's paper to compare but only one Gauss's. The AGM suffices for calculating complete elliptic integrals of the first kind. And, in fact, Adlaj's paper provides a conceptual geometric interpretation to Gauss's method for calculating the complete elliptic integral of the second kind and that's why Gauss is so repeatedly emphasized up to Brent-Salamin method which turns out again to be due to Gauss. The significance of Gauss's method was not well understood before Adlaj's paper appeared. There is no Carlson's method here, as you wrote for your first implementations since it is really Gauss's, and there is no point in arguing about the state of the art of calculating elliptic integrals without accurately pinpointing individual contributions. It seems to me that the concept of MAGM which was introduced by Adlaj for the complete elliptic integrals of the second kind or for some other purpose, regardless of the method you use to calculate it, was misunderstood by you and @Jrheller1: and thus unjustly treated. Instead, it must be stated with pointing out the two ways of calculating it, the equivalence of which is proven in the reference to Mathematics Stack Exchange given above. That would further clarify the issue instead on confusing it. So, to summarize, Adlaj's formula is a compact expression for the circumference of an ellipse which turns out to have a geometric interpretation as ratio of MAGM to AGM and we must keep in mind that calculating the ratio is based on Gauss's method. So, I would say it is Adlaj's formula and it is Gauss's method. Sorry Carlson and Brent. 83.149.239.125 (talk) 10:31, 27 September 2018 (UTC)

83.149.239.125: I'm not really sure what your point is. So let me address a couple of questions concerning the circumference section of this article.

1. What is the best method of evaluating the circumference in terms of the elliptic integral?
2. Who should get credit for this in this article?

For 1, the reader is pointed to Carlson's 1995 paper and a link to some python code implementing the method in that paper (this is the python function carlson above). This is simpler, faster, and more accurate than Adlaj's method. There's no reason to confuse the reader by steering her to Adlaj's method.

For 2, the reader is left going to the Wikipedia articles complete elliptic integral of the second kind, Carlson symmetric form, arithmetic-geometric mean. I think this is appropriate for this article on ellipses. Adlaj's relatively recent (2012) paper doesn't need to be included. Perhaps you are saying that Gauss is being short-changed? This is always an issue for topics in mathematics once they enter the mainstream. However, the fact of the matter is that Gauss' contributions to the AGM are well documented; I note that Carlson (1971) includes a detailed history of the AGM. Regardless, this article is not the place to have this particular discussion.

cffk (talk) 21:05, 27 September 2018 (UTC)

cffk (talk) questions indicate that the single link provided was ignored, so I repost it for its crucial importance https://math.stackexchange.com/questions/391382/modified-arithmetic-geometric-mean. Both questions were anticipated and answered. Of course, there is only one best method for calculating the circumfernce of an ellipse. It is Gauss's method which you should not call Carlson's. There is no convincing "philosophical" justification for "short-changing" Gauss's method, as you are not obliged to call this original method, based on AGM, after anyone other than Gauss. We have NO Carlson's method here to be discussed. There is, however, Adlaj's formula for the circumference of an ellipse as ratio of two "means". Being a ratio, it must be calculated via Gauss's method as told in Adlaj's paper and further explained in the link which you must see. Calculating the ratio does not restrict you to calculating the numerator and the denominator separately. That calculation completely coincides your first implementation which you keep on wrongfully calling Carlson's method. The additional concept of the modified arithmetic-geometric mean is however important for its own sake as it can be used in other physical applications such as calculating the length of a tether in a linear parallel field of repelling forces as told in another freely available Adlaj's paper http://www.ccas.ru/depart/mechanics/TUMUS/Adlaj/ImaginaryTension16.pdf. Your second implementation and the definition of MAGM would then become relevant since the AGM no longer appears in the denominator, as you can tell, if you'd be as keen as to look up that second paper. The calculation then may resemble your second implementation. So, sorry again, Adlaj's contribution is more important than you care to admit whereas Carlson need not necessarily be mentioned here. That answers your second question. Yet, I have no strong feelings concerning this issue as I was not as lazy to dismiss your link to Calson's 1971 paper which I find quite nice but irrelevant to our discussion. So please do look up what I am sending you before you reask and find all your questions already answered. I know you would not be able to read the story on the origin of MAGM since it's not available in English. But just in case I'm wrong I'll give you the link to a Russian book https://www.morebooks.de/store/gb/book/%D0%A0%D0%B0%D0%B2%D0%BD%D0%BE%D0%B2%D0%B5%D1%81%D0%B8%D0%B5-%D0%BD%D0%B8%D1%82%D0%B8-%D0%B2-%D0%BB%D0%B8%D0%BD%D0%B5%D0%B9%D0%BD%D0%BE%D0%BC-%D0%BF%D0%B0%D1%80%D0%B0%D0%BB%D0%BB%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D0%BC-%D0%BF%D0%BE%D0%BB%D0%B5-%D1%81%D0%B8%D0%BB/isbn/978-3-659-53542-0. 83.149.239.125 (talk) 12:40, 28 September 2018 (UTC)

Please don't get too hung up on my using "Carlson's method" and "Adlaj's method". This was just a convenience for the present discussion. Let's call them "Gauss' method as given in Carlson (1995)" and "Gauss' method as given in Adlaj (2012)". Similar, let's rename the two python functions "carlson" and "adlaj" as "gauss1" and "gauss2", respectively.

I gather that you're happy to promote "gauss1" as the "best" way to compute the perimeter. Given this, I don't see any reason to change this article. Specifically, it's not appropriate to include a reference to Adlaj (2012). (For one thing, I was happily using "gauss1" in 2009 three years before Adlaj's paper.) Perhaps, as you indicate, there are reasons to investigate the Adlaj's MAGM separately. But that's beyond the scope of this page.

It is unfortunate that Adlaj's paper is built on the false premise, that, prior to his paper, there was no known adaption of the AGM to compute the elliptic integral of the second kind. So any citation of the paper really requires an asterisk to point out this problem with priority. (Ideally, the author would have supplied a corrigendum to his paper.) I have E-mailed Adlaj to alert him to this discussion, in case he wants to weigh in.

cffk (talk) 14:25, 28 September 2018 (UTC)

Later: in researching later works by Adlaj I came across An arithmetic-geometric mean of a third kind with this alarming statement at the end: "Profit-seeking organizations, including commercial software companies and their representatives, must address the author for an explicit written permission, without which they are never permitted to use any formulas, algorithms or methods based on the concept of MAGM or GAGM." This would seem to preclude some research on the MAGM. However, I've no idea how the author expects a retroactive condition on his 2012 paper to be enforceable! cffk (talk) 14:58, 28 September 2018 (UTC)

Yes, I did find that alarming statement. But the preceding statement said that "The author supports an unrestricted access to knowledge, and grants his permission for using his algorithms and formulas to persons and non-profit-seeking organizations." Incidentally, at the bottom of page 7 of this "third" Adlaj's paper, we can once more run across the recursive formula which we would "happily" name Gauss's method 1. Adlaj's paper seems to be based on the premise that Gauss's exceptional method was not well understood before introducing the MAGM which clarified the iterative nature of calculating complete elliptic integrals of the second kind. Not only we can obtain a quadratically convergent lower and upper bound for our integral but we can obviously and clearly combine iterations to produce quartic or higher convergence. It refuted the falacy that "no simple exact formula for calculating the perimeter of an ellipse exists". And, as we now know, the ratio of complete elliptic integrals arises quite frequently in practical applications. This ratio is MAGM in the case we are discussing and, more generally, it's GAGM. So that the recursion at the bottom of page 7 is only a special case of a recursive formula for calculating complete elliptic integrals of the third kind which applies to the second kind. Indeed, the concepts of MAGM and GAGM provide the last clarifying straw for the full understanding of Gauss's method and for the exploration of its symmetries. We need not cripple ourselves with avoiding the MAGM point of view. As for false premises, then this paper with its "overwrought" title A New and Wonderful Pendulum Period Equation must win your "grand prize". According to its author, Gauss's mathod "was discovered in 2008" by two authors who, as the title of their paper says Approximations for the period of the simple pendulum based on the arithmetic-geometric mean, did not even understand that Gauss's formula was exact, not approximate. Strangely enough, Adlaj's paper is mentioned without understanding that Adlaj, on page 1097 of his paper in the Notices, which we are doing our best in not mentioning, gave Gauss all the credit for that "new and wonderful pendulum period equation" and dated it more than two centuries earlier May 30, 1799. I'd join the wishing that Adlaj himself would "weigh in" but I fear that he could have his reasons not to. So let's keep this discussion ongoing and keep our fingers crossed. 83.149.239.125 (talk) 12:34, 1 October 2018 (UTC)

Let me try to summarize the state of play.

The question is whether Adlaj's contributions to the study of complete elliptic integrals should be acknowledged in this article. Adlaj's first paper on the subject An eloquent formula for the perimeter of an ellipse appeared in 2012 in Notices of the AMS. He wrote a second paper An arithmetic-geometric mean of a third kind!; this is unpublished and undated(!) -- however it appeared to have been written in 2015.

Prior to 2012, there were two indispensable sources of information on special functions.

• Abramowitz and Stegun (1964). Chapter 17 by Milne-Thomson covers elliptic integrals and Equations 17.6.3 and 17.6.4 show how the AGM can be used to compute the complete integrals of the 1st and 2nd kinds.
• Olver et al., NIST Handbook of Mathematical Functions (2010). Chapter 19 by Carlson covers elliptic integrals and Equations 19.8.5, 19.8.6, 19.8.7 give AGM formulas for the complete integrals of the 1st, 2nd, and 3rd kinds. (The first two formulas just repeat those in Abramowitz and Stegun with some changes in notation.) These formulas appear in Section 19.8(i) "Gauss's Arithmetic-Geometric Mean (AGM)".
• Several sources are given in this section for the NIST Handbook. The first is Cox, The arithmetic-geometric mean of Gauss (1984), which includes a detailed chronicle of Gauss's contribution to the subject.
• Both A+S and the NIST Handbook give (essentially) the same formula for the second integral. It (first?) appears in this form in King, On the direct numerical computation of elliptic functions and integrals (1924), p. 39, who references Gauss's Collected Works, Vol 3. (Page 42 of King's book makes the explicit connection to the circumference of an ellipse.) (Update: Cayley, Elliptic Functions (1876), p. 331 also gives the same result. cffk (talk) 18:41, 4 October 2018 (UTC))

So if I were to suggest an update to the section on the circumference of an ellipse from the pre-2012 vantage point, I would recommend (update made cffk (talk) 13:33, 5 October 2018 (UTC))

The circumference of the ellipse may be evaluated in term of the complete elliptic integral of the second kind using Gauss's arithmetic-geometric mean (cite NIST Handbook + Python code).

How does Adlaj's 2012 paper change this situation. Surely the answer is "not at all". His main result, the method for the second integral, is well known (even though he writes it in a new way); indeed it is included in his reference to A+S. A secondary goal of his paper is to highlight Gauss's role; but here again, this is already well documented by King (1924) and Cox (1984). It's somewhat of a mystery to me how Adlaj could have overlooked the prior work. It's unfortunate that he relies on what is a clearly a somewhat suspect source for his assertion that the problem was (as of 2012) unsolved. However, I know that in the excitement of discovery it's easy to rush to print.

But this does not excuse Adlaj's doubling down on his error in his 2015 paper. Here he indirectly acknowledges that A+S includes the result for the second integral "the section ... was not extended to calculating elliptic integrals of the third kind" (leaving the reader to intuit that it was extended to compute the second integral). He writes that the NIST Handbook also includes a result for the third integral (the main object of his 2015 paper), but he muddies the waters by referring to the online version with a release date of 2015-08-07 even though the printed version of 2010 includes the result, suggesting that he might have found the result independently

cffk (talk) 19:24, 3 October 2018 (UTC)

The said above by cffk is utterly ridiculous. He is leaving us to “intuit” that the calculation of “third integral” was not known to Gauss but was given two centuries later around “2010”. The object of Adlaj’s 2015 paper was GAGM which generalized the AGM and the MAGM and provided a unified geometrical interpretation of Gauss method for calculating elliptic integrals of all three kinds. Adlaj’s paper singles out Gauss’ contribution and eliminates any incinuations and vague suggestions which attempts to undermine that contribution. Cocorrector (talk) 21:23, 28 November 2018 (UTC)

I've been studying the ellipse perimeter equation for a couple of years ... but I'm new to editing wikipedia. I'm curious, if there was an analytical equation that gave a result close to exact (100+decimal digits) wouldn't that be worth having in the article even as a footnote? Why is there such a fuss over the AGM or MAGM which is an iterative solution ?

I mean, I've been working on an approximation formula since college in 1985 ... and I have no way to even know if someone else has published my idea before me. It's not like I care to take the whole credit for the idea, but I also don't want to start an uproar over "who came up with this first." I mean -- I've got a math professor as a friend who commented that he read a book someone's supposedly solved the ellipse equation *exactly*. But, this entire argument thread seems to imply that no such formula exists (or else, no one believes it does ... )

I wouldn't want to publish a simple one-liner formula on wikipedia -- just to have people start a war over who came up with the idea first. It's quite easy to verify if a formula gives the correct answer to the number of digits in your above AGM/MAGM programs SO, it's not about whether the formula is fake/pseudo-science/pseudo math -- as Wikipedia memebers can verify it -- but how does wikipedia decide what is "novel" and "new" vs. what's (more likely) re-invention of an old idea ?

IN Richard Feynman's famous lectures on physics, he credits a few equations that he himself derived to others !! Feynman just puts in the foot notes, "I wasn't aware of the prior equation when I derived mine."

Is there a place on wikipedia for testably correct formulas where there "might" be a predecessor 100+ yeaars ago?

In the publishing world it must be tempting to try and fake a back-copyright to information stolen from others. Publishing useful information on wikipedia is a problem when it gets people's ego's involved, and I wouldn't want to invite lawsuits. :)

24.21.255.187 (talk) 08:06, 23 April 2020 (UTC)

Everything stated on Wikipedia must be verifiable and noteworthy.—Anita5192 (talk) 16:26, 23 April 2020 (UTC)

Talk:Ellipse: semi-lattice rectum.

If this is a repeat submission, I apologize. For some reason it didn't get added yesterday.

The radius of curvature (as opposed to curvature k) is generally defined as the radius of a circle that fits tangent to a graph at a vertex.

In the Ellipse article (and in the hyperbola article), the semi lattice rectum is defined as a length that is the radius of curvature. (see Section 2:2:4) This has to be a mistake of some kind ... for the images and hyperlinks in the ellipse article show a correct definition of radius of curvature and osculating circles by hyperlink; However, in the common image showing the semi-lattice rectum for conic sections having a common vertex and semi-lattice rectum (called 'p' or cursive 'l'); clearly the semi-lattice rectum of the ellipse is LARGER than the radius of curvature for the circle in the same image. Clearly, the focus of the ellipse can NOT coincide with the origin of the circle ... so the semi-lattice rectum and the radius of curvature for an ellipse can not be the same size.

But that's what section 2.2.4 implies by it's wording about "radius" of curvature.

How do we go about deciding which to correct, the picture or the text? Andrew3Robinson (talk) 21:00, 23 April 2020 (UTC)

The statement "The semi-latus rectum $\ell$ is equal to the radius of curvature of the osculating circles at the vertices." does not appear correct, so I appended a {{Citation needed}} template. If no one cites this statement in a reasonable amount of time, the statement can be removed. I also cited Protter & Morrey for the statement that

$\ell ={\frac {b^{2}}{a}}=a\left(1-e^{2}\right),$

which is correct.—Anita5192 (talk) 22:21, 23 April 2020 (UTC)

The disputed statement is correct. Please see any text book on this subject. (I have only access to German books). I deleted "osculating circle". "radius of curvature" is enough.--Ag2gaeh (talk) 08:25, 24 April 2020 (UTC)

3D rotation

Let’s say we want to represent an ellipse in the three-dimensional space. If it’s centered at the origin and in the (x, y) plane, then its equation is obviously (x²/a²)+(y²/b²)+z=1, where z would be zero if it’s on the (x, y) plane and any real number if it’s parallel to the (x, y) plane.

Now, let’s rotate and move our ellipse on the (x, y) plane or parallel to it, by (X, Y) and angle θ. (This is equivalent to a rotation around the z axis.) We thus have:

{[(x-x₀)cosθ+(y-y₀)sinθ]/a²}+{[(x-x₀)sinθ+(y-y₀)cosθ]/b²}+z=1

which is basically what we have on the main page.

But what if our ellipse is also rotated around the x axis or around the y axis? Or even around both of these axes. Let’s call these angles φ (rotation around the x axis) and ξ (rotation around the y axis).

What would we get? My math skills are not advanced enough to get there, so I would appreciate any help possible.

Thanks in advance!

CielProfond (talk) 21:23, 16 August 2020 (UTC)

double check

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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check the math it does not add up so I changed it the original was Area = $Piab$ I changed it to Area = $Pi(a+b)^{2}$ because $Pib^{2}$ when stretched by a factor of $a/b$ did not match the scale of the area by the same factor $Pib^{2}(a/b)=Piab$ relevant to $a/b$ with a starting radius (r) of 3 $r=3$ — Preceding unsigned comment added by 2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 18:16, 24 September 2020 (UTC)

It is incorrect. The previous formula $\pi ab$ was the correct one. Your formula, $\pi (a+b)^{2}$, is the area of a much bigger circle with radius $a+b$ surrounding the ellipse. —David Eppstein (talk) 18:35, 24 September 2020 (UTC)

You are Half right I already made the mistake so I won't try changing it again however check the math use the radius value 3 the equation is wrong but this one is right $Pi(a+b)/2$ a radius of 3 with the stretch factor $a/b$ a=2 b=4 keep in mind there are two radii now $(a+b)/2=3$ that is the original of 3 so $Pib^{2}=Pi(a+b)/2$ it was my mistake I multiplied instead of dividing if $Pi8$ Pi does not = 1.2275 if you changed the value of Pi then it works but Pi is a constant it is the relation to how many time the radius of a Circle will wrap around the perimeter I know algebra and I know how people that use algebra to solve simple equations make mistakes just like I did multiplying instead of dividing but this boils down to the value of Pi.19dreiundachtzig (talk) 20:07, 24 September 2020 (UTC) — Preceding unsigned comment added by 2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 19:40, 24 September 2020 (UTC)

No, your math is still wrong. This is a very widely known formula, consult any algebra textbook if you're having trouble. - MrOllie (talk) 19:49, 24 September 2020 (UTC)

what is the value of Pi maybe you know algebra but do you know how to do basic math19dreiundachtzig (talk) 20:10, 24 September 2020 (UTC)

What do you think is more likely? a) Your math is incorrect b) Every algebra textbook on the market is incorrect. - MrOllie (talk) 20:24, 24 September 2020 (UTC)

What year was your textbook written I think stretch factor is someone else's technique and not being used properly this article has bean changed so many times there's always a different equation and a new textbook the underline principal of stretch factor is that an ellipse is an elongated circle nothing more2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 20:38, 24 September 2020 (UTC)

I'm going to make this simple the source is not cited cite the source or I delete it you have one week to cite the source or I will deleted it on 10/01/20 — Preceding unsigned comment added by 2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 20:50, 24 September 2020 (UTC)

Let's be clear here: You are challenging that the area of an Ellipse is $\pi ab$? You would like a citation for that? - MrOllie (talk) 20:56, 24 September 2020 (UTC)

No not just a citation for $Piab$ but the stretch factor in relation to the equation show the value of $a$ and $b$ if you can't prove that stretch factor has actual values as you would in algebra just like any algebra equation if you cant prove the stretch factor or the values are true then I will just delete that and leave the rest2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 21:10, 24 September 2020 (UTC)

Ok, citation added! - MrOllie (talk) 21:26, 24 September 2020 (UTC)

Thank you for adding a citation I can't access the material from the link I will check my University Library later to see if they have it you said pg.115 I hope this is not just the area equation because what I am challenging is weather or not the area equation coincides with the stretch factor equations without changing the value of Pi as determined by non other than Archimedes the person you cited2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 21:46, 24 September 2020 (UTC)

okay this is just area it does not mention the stretch factor maybe you think I will just see something that is not there if that is what you were trying to do you seceded what do you think about deleting the stretch factor part and just adding some type of definition about area and Pi maybe it could held set a example or outline to me it seems the author uses Pi without understanding it I could change the value of Pi and this explanation of stretch would work and tie up everything that is being held together so loose.2601:203:101:BD0:78F1:5839:7DCC:FC03 (talk) 23:28, 24 September 2020 (UTC)

It is clear that there is something about this article that you don't understand, and that your suggestions for change to the article make no sense, but it is also possible that your lack of understanding is caused by something in the article that is more confusing than it needs to be. Unfortunately, you are also not expressing yourself at all clearly, so I can't tell what might be confusing you. A starting point might be learning to punctuate sentences. —David Eppstein (talk) 23:59, 24 September 2020 (UTC)

I'm trying to submit changes through the sandbox here is a preview Where $a$ and $b$ are the lengths of the semi-major and semi-minor axis, respectively. The area formula is intuitive start with a circle of area $b$ and scale it by a factor of $(a>b)$ to make an ellipse, this scales the area by the same factor of π$b^{2}$=π$(a>b)$19dreiundachtzig (talk) 00:18, 25 September 2020 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Gatekeeping

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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This article has allot of gatekeeping. I would love to discuss improvements with out being attacked by gatekeepers 10 years ago when there was no mention in this article about a Ellipse being an Elongated Circle I was attacked by a Gatekeeper when I said an Oval is just an elongated Circle because I said Oval and not Ellipse now the article is littered with the Idea of Elongation. The improvement I would like to see is $(r)$ used for radius Under the Area section you see the equation π$b^{2}$ in the main article for Circle (r) is used Second improvement I would like to see is the use of brackets in the Area equation π$ab$ I think it should look like this π$(ab)$ thank you for taking the time to consider these improvements please keep an open mind.19dreiundachtzig (talk) 02:06, 27 September 2020 (UTC)

Can you link the sandbox you're referring to? I'm having trouble understanding your point. You want r rather than a and b? That would not be consistent with the rest of the article, or with how ellipses are usually described. And you want parentheses around the ab after π? Why? Dicklyon (talk) 21:51, 27 September 2020 (UTC)

He's a crank. He wants to replace the correct area formula by an incorrect one. See the discussion above and recent edits to the article. —David Eppstein (talk) 23:23, 27 September 2020 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

"Crank" doesn't help us move forward though. He might be back, complaining more about how he can't say his bit. Challenging him to explain himself seems worth doing, but requires waiting on his response, to see if the confusion behind it can be revealed. Dicklyon (talk) 04:29, 29 September 2020 (UTC)

Well, if he wants to replace the correct formula with an incorrect/unclear one, then someone then go warn him about disruptive editing. ~ Destroyeraa🌀 12:34, 29 September 2020 (UTC)

@Dicklyon: This guy has "explained" themselves far more times than is necessary, and has been at this for years. It's a lost cause.--Jasper Deng (talk) 16:48, 29 September 2020 (UTC)

The comments left above and on my user talk do not make me hopeful for an explanation that reveals anything intelligible. —David Eppstein (talk) 16:56, 29 September 2020 (UTC)

On an area formula, contribution of B. Gottschalk

The area formula inserted by User Bernard Gottschalk can be seen as a consequence of a theorem of Apollonius on conjugated half diameters of an ellipse (see Bronshtein and Semendyayev, or https://de.wikipedia.org/wiki/Satz_von_Apollonios) or can be calculated straight forward (see section Theorem of Apollonios on conjugate diameters).--Ag2gaeh (talk) 15:53, 2 February 2021 (UTC)

Finding the foci and directrices geometrically

Ellipse: definition by focus and circular directrix

Ellipse: definition by focus and linear directrix

Hyperbola: definition by focus and linear directrix

Here are some ways to find the focus (point F) and directrix (line through D) using compass and straight edge. Didn't see them mentioned in the article. I would create an animation but my software is not that good. ➧datumizer  ☎  10:47, 2 March 2021 (UTC)

Your method is just a variation of the method shown in the picture of subsection "standard equation" and the fact, that a directrix and the corresponding focus are a pair pole-polar.--Ag2gaeh (talk) 13:21, 2 March 2021 (UTC)

Maybe I am looking at the wrong image? I don't see any similarity. ➧datumizer  ☎  20:45, 3 March 2021 (UTC)

The article says, "C2 is called the circular directrix (related to focus {\displaystyle F_{2}}F_{2}) of the ellipse.[1][2] This property should not be confused with the definition of an ellipse using a directrix line below." So the two images describe different things. ➧datumizer  ☎  21:30, 3 March 2021 (UTC)

Shape parameters

I mentioned the picture in subsection "standard equation". Any construction of a focus uses the equation $a^{2}=b^{2}+c^{2}$ and a right angular triangle, Yours too. Your construction of one point of the directrix line is based on the fact, that the points $(c,0),({\tfrac {a^{2}}{c}},0)$ are inverse with respect to circle $x^{2}+y^{2}=a^{2}$. This is equivalent to a pole-polar relation (see section of this article) with respect of this circle.--Ag2gaeh (talk) 08:06, 4 March 2021 (UTC)

The image doesn't actually show how to plot the points geometrically though. Yeah it is possible to infer this. But is it maybe better to show instead of tell? Or is there a length limit on Wikipedia articles? ➧datumizer  ☎  05:31, 6 March 2021 (UTC)

If You agree, I add Your picture to section "pole-polar relation". But, it would be suitable to cut off not necessary parts and to add the lines containing the main axes. The usual construction of focus F (see picture) is more easy, so You should concentrate on the construction of point D and the directrix (orthogonal to line OD). --Ag2gaeh (talk) 08:48, 6 March 2021 (UTC)

What parts are unnecessary? I don't understand. I have created a similar image for the hyperbola (see to the right) and would like to keep as many elements as possible the same between them. I also can create two separate sets of images for the ellipse and hyperbola: one set for constructing the focus, another set for constructing the directrix. ➧datumizer  ☎  06:00, 8 March 2021 (UTC)

With "unnecessary" I meant just "white space" to shrink the picture a little. For the hyperbola it is the same game: F and D are inverse with respect of the green circle. In both cases You should add the lines of the great main axis, on which the points F,D,A lie. Please insert Your pictures together with some explanations in a suitable subsection.--Ag2gaeh (talk) 14:34, 8 March 2021 (UTC)

Error in formula for 'F' - the intercept in terms of semimajor and semiminor?

Formula reads

$F=Ax_{0}^{2}+Bx_{0}y_{0}+Cy_{0}^{2}+a^{2}b^{2}$

But the a and b here are different from the a and b in the other equations - they should be doubled, no? I found the formula to end with $4a^{2}b^{2}$.— Preceding unsigned comment added by 88.109.89.43 (talk) 23:21, 23 August 2021 (UTC)