Wikipedia:Reference desk/Archives/Mathematics/2016 May 30

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May 30

Diffy qs

One year with a math-major dorm roommate left me with a few bits of math-major slang, including "partial diffy qs" for a class he was taking during one semester. I'm wondering whether "diffy q" would be a good {{R from slang}} redirect to differential equation, and "partial diffy q" to partial differential equations? I found some online references to the concept, but I don't know whether it's really a common phrase, and even if it is, I don't know how it's most commonly spelled. Nyttend (talk) 00:04, 30 May 2016 (UTC)

differential equation already has a bunch of redirects in this area, and there doesn't seem to be a problem with you adding more variant spellings. --Tagishsimon (talk) 00:17, 30 May 2016 (UTC)

Are you sure you didn't mishear your roommate saying "diff eqs"? A straight Google search on the quoted string "diffy qs" claims to yield "About 3,390 results", but that is a notoriously unreliable figure (on top of the questionable relevance of the actual count), and when I repeatedly request the "Next" set of results, it ends with page 17 being a partial page of results, claiming that it found only "about 166 results". Also, it appears that the majority of those results are references to one particular 2014 publication entitled Notes on Diffy Qs. This does not strike me as common slang, and my expectation is that when it is used it would most commonly be when making fun of a layperson misunderstanding math-speak. -- ToE 01:53, 30 May 2016 (UTC)

Thank you. This is precisely why I said I don't know how it's most commonly spelled; it's very easy to misspell something when you've only heard it, and I'm glad I didn't create something based on my mishearing. Nyttend (talk) 02:00, 30 May 2016 (UTC)

"Diff eq" is a very common phrase (or spoken abbreviation), and it is said without any pause after the "diff", so it does sound just like "diffy q". While I wouldn't propose such a redirect, I suppose it could be an {{R from misspelling}}. --- ToE 03:15, 30 May 2016 (UTC)

No objection to the redirect, but I don't think it sounds exactly the same — I think "diff EQ" is pronounced with the E stressed, whereas the second syllable of "diffy" would not be stressed. --Trovatore (talk) 04:37, 3 June 2016 (UTC)

What is a 'grim reaper curve'

At the end of the second paragraph of the Wkipedia article titled Curve-shortening flow it says:

The circle is the only simple closed curve that maintains its shape under the curve-shortening flow, but some curves that cross themselves or have infinite length keep their shape, including the grim reaper curve, an infinite curve that translates upwards, and spirals that rotate while remaining the same size and shape. [I have bolded relevant part.]

Can someone please describe in more detail what is this 'grim reaper curve'? (It has no Wikipedia article.)

(I would have thought the grim reaper curve to be a finite curve in the shape of a scythe blade, rather than 'an infinite curve that translates upward', but apparently it's not.)Bh12 (talk) 07:18, 30 May 2016 (UTC)

Have you looked at Curve-shortening flow#Curves with self-similar evolution section? It says the grim reaper curve is $y=-\log \cos x$. --CiaPan (talk) 10:17, 30 May 2016 (UTC)

For another time, many browsers can search the current page for a string with Ctrl+F. PrimeHunter (talk) 10:31, 30 May 2016 (UTC)

Thanks for the answer and for the Ctrl+F hint!

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