Maxima: Differentiate sum at specific index-position
Subject: Maxima: Differentiate sum at specific index-position
From: Pepe Sanchez
Date: Tue, 7 May 2013 12:52:25 +0200
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
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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
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