Re: Differentiation w.r.t. elements of lists

*To*: mathgroup at smc.vnet.net*Subject*: [mg79712] Re: Differentiation w.r.t. elements of lists*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Thu, 2 Aug 2007 03:54:58 -0400 (EDT)*Organization*: Uni Leipzig*References*: <f8pi48$1l4$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de

Hi, and you are shure that > Another, even shorter test case would be > > D[x[[i]], x[[j]]] > > which "should", IMHO, return KroneckerDelta[i,j]. ?? Than D[x[[1]],x[[2]]] should be zero ? right ?? but what is with x = {Sin[y], y} D[x[[1]], x[[2]]] the result is not 0 .. may be that you are wrong. Regards Jens Daniel Hornung wrote: > Hello, > I don't know if what I want to do is impossible to do neatly (probably not) > or whether I simply chose the wrong way (maybe). > > Basically I want to do componentwise differentiation. Here's a short test > case: > ---- > In[1] := h[x_]:=Sum[x[[j]]^2,{j,1,Length[x]}] > > In[2] := dh[x_,i_]=D[h[x],x[[i]]] >>From In[2]:= > Part::pspec: Part specification i is neither an integer nor a list of > integers. Mehr... > Out[2]= 0 > > In[3]:= Assuming[i\[Element]Integers&&i>0&&i<=n,dh[x_,i_]=D[h[x],x[[i]]]] >>From In[3]:= > Part::pspec: Part specification i is neither an integer nor a list of > integers. Mehr... > Out[3]= 0 > ---- > > What I would want is a result like dh[x_,i_]=2x[[i]], of course. > > Another, even shorter test case would be > > D[x[[i]], x[[j]]] > > which "should", IMHO, return KroneckerDelta[i,j]. > > Any ideas or hints how to solve these problems in a nice way? > > Thank you in advance, > Daniel Hornung >