ASKSAGE: Sage Q&A Forum - RSS feedhttps://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Wed, 13 Jul 2011 12:26:39 +0200summing over a list of variables?https://ask.sagemath.org/question/8222/summing-over-a-list-of-variables/Hi all,
I'm new to SAGE (I'm trying to move over from Mathematica), and I was wondering if someone could help me define the following function:
$$ r_k(x_1, x_2, x_3, x_4) = \left( \sum_{i=k+1}^{4} x_i^2 \right)^{1/2} $$
I figured I could do something like:
var('k,j', domain=NN)
x = [var('x_{index}'.format(index=i)) for i in range(4)]
r(k,x) = sqrt( sum( x[j]^2, j, k, 3 ) )
But this returns the error:
> TypeError: unable to convert x (=j) to
> an integer
Worse yet, when I enter sage:x, it returns x, and forgets x was a list of variables. And to complicate things, when I try
y = [1,2,3]
sum( y[j], j, 0, 1)
I get the error
>TypeError: unable to convert x (=j) to an integer
even after I do "clear_vars()" and try everything all over again.
Can anyone tell me what's going on?StevenPollackWed, 13 Jul 2011 12:26:39 +0200https://ask.sagemath.org/question/8222/