Re: How to use "Apply" to do differentiation ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg114460] Re: How to use "Apply" to do differentiation ?*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Sun, 5 Dec 2010 21:49:53 -0500 (EST)

Why are you surprised at the result? Recall that what Apply[fn, expr] does is to replace Head[expr] by fn and then evaluate that. For simplicity, let's use the name: d = D[#, x] & Now Head[x^5] is Power, so the result from Apply[d, x^5] is the same (as your trace will show you) as that from D[x,x], which is of course 1. I presume the whole point of what you were doing was to use a name for the first-derivative operator. Why not just the following? d[x^5] On 12/4/2010 6:16 AM, 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? > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305