Re: Derivative of Sum
- To: mathgroup at smc.vnet.net
- Subject: [mg47935] Re: Derivative of Sum
- From: bghiggins at ucdavis.edu (Brian Higgins)
- Date: Fri, 30 Apr 2004 19:27:38 -0400 (EDT)
- References: <c6q28u$p5l$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Michal,
I s this what you want:
S[p_] := Sum[a[k]b[k], {k, 1, p - 1}] + a[p]b[p] + Sum[a[k]b[k], {k, p
+ 1, n} ]
In[3]:=D[S[5],b[5]]
Out[3]=a[5]
Note that differentiating a series term-by-term may not always give
you the incorrect answer.
Cheers,
Brian
"Michal Kvasnicka" <michal.kvasnicka at _NO_ZpaMM-.quick.cz> wrote in message news:<c6q28u$p5l$1 at smc.vnet.net>...
> Is Mathematica 5 able to compute the folowing problem:
> \!\(S = Sum[\(a\_k\) b\_k, {k, 1, n}]\)
>
> then should be
>
> \!\(\[PartialD]\_\(a\_i\)\ S = b\_i\) but the Mathematica gives 0.
>
> Thanks, Michal