Re: How to use "Apply" to do differentiation ?
- To: mathgroup at smc.vnet.net
- Subject: [mg114500] Re: How to use "Apply" to do differentiation ?
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sun, 5 Dec 2010 21:57:16 -0500 (EST)
On 4 Dec 2010, at 12:16, Mayasky wrote: > Something simple yet unbelievable occurred when I use: > > Apply[D[#, x] &, x^5] > > The output is invariably 1 whether I use x^5 or x^100. > Also I suggest you to try "Trace" command to see > the weirdness -- the output is messy if pasted as > text here. > > Finally I have to take a detour and use: > Nest[D[#, x] &, x^5, 1] > > I have been using Mathematica for several years and > never found that. I myself is wordless, but can anyone > explain that? > I don't see anything very strange in this. Note that the full form of x^5 is Power[x,5]. Observe that in general Apply[f[#] &, p[x, y]] f(x) So not Apply[D[#,x]&,Power[x,5]] will give D[x,x] which is 1. What I do not understand is what you actually intended to achieve. If you wanted simply to differentiate x^5 the way to do it is D[#, x] &@(x^5) or (if you really must): Compose[D[#, x] &, x^5] 5 x^4 Andrzej Kozlowski