Re: Differentiation w.r.t. elements of lists
- To: mathgroup at smc.vnet.net
- Subject: [mg79762] Re: Differentiation w.r.t. elements of lists
- From: Daniel Hornung <ds.mpg.de.thispartismydomain.daniel.hornung at insertdomainhere.com>
- Date: Fri, 3 Aug 2007 06:38:04 -0400 (EDT)
- Organization: GWDG, Goettingen
- References: <f8pi48$1l4$1@smc.vnet.net> <f8s3e2$38u$1@smc.vnet.net>
- Reply-to: ds.mpg.de.thispartismydomain.daniel.hornung at insertdomainhere.com
Jens-Peer Kuska wrote:
> 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
>
OK, I think I had thought wrongly there. But sadly that still doesn't
answer my main question:
Why does the second line result in 0, and what could I do better?
>> h[x_]:=Sum[x[[j]]^2,{j,1,Length[x]}]
>> D[h[x],x[[i]]]
--
Daniel Hornung
Max Planck Institute for Dynamics and Self-Organization
G=C3=B6ttingen, Germany