Maxima: Differentiate sum at specific index-position
Subject: Maxima: Differentiate sum at specific index-position
From: Stavros Macrakis
Date: Tue, 7 May 2013 10:18:12 -0400
Doing this really isn't that hard in principle, but as far as I know, no
one has actually done it. See
http://www.math.utexas.edu/pipermail/maxima/2011/025302.html
This seems to come up once a year or so... maybe we should do something
about it.
-s
On Tue, May 7, 2013 at 6:52 AM, Pepe Sanchez <jose.sanchez at uv.es> wrote:
> Benjamin Steinvorth wrote:
>
> in Maxima 12.04.0 I have a sum
> mysum : sum(u[i]^2, i, 1, N);
>
> now I differentiate it
> diff(mysum, u[i]);
>
> now I specify a defined index i=A to differentiate it at
> at(%, i=A);
>
> Unfortunately maxima won't replace the u[i] in the sum that way.
> How can I bring maxima to a result like
> 2*u[A]
>
>
> In my opinion, a CAS hardly can hand a particular value for an index in a
> general expression like that.
> Perhaps you can individualize your particular term of index A this way:
>
> --> mysum : sum(u[i]^2, i, 1, N-1)+u[A]^2;
>
> (%o1) u[A]^2+sum(u[i]^2,i,1,N-1)
>
> --> diff(mysum, u[A]);
>
> (%o2) 2*u[A]
>
> FWIW
> Best
>
> Pepe
>
> _______________________________
> _________________________________
> Jose Sanchez-Marin.
> Universitat de Valencia.
> Institut de Ciencia Molecular (ICMol).
> Cat. Jose Beltran Martinez, 2 Phone: +34 96 354 4444
> E-46980 Paterna FAX: +34 96 354 3576
> Spain e-mail: Jose.Sanchez at uv.es
> _________________________________________________________________
>
>
>
>
> _______________________________________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/mailman/listinfo/maxima
>
>