On Sun, 30 Jan 2011 19:04:38 +0100
Francois Maltey <[email protected]> wrote:
> Hello,
> > I'd like to plot this function of x (latex code):
> >
> > x/2 + sum_{r=1}^n cos(rx)
> >
> > for some fixed n.
> //A//
>
> First, sum is designed for formal sum, not for truncate sum even if
> sometimes it's possible.
> But add is designed for these sums.
>
> Second, expression doesn't evaluate the add(...) function.
>
> Third, I think you want to change n0...
>
> So I propose a function s (in Python), not a function coming from
> expression.
>
> k = var('k');
> def s(x,n) :
> return x/2 + add (cos(k*x) for k in [1..n])
>
> n0 = 5;
> plot(s(x,n0),(x,0,pi))
>
> //B//
>
> You use Sage, not Maple. You must forget semicolon at the end.
>
> //C//
>
> After var('n'), it seems that your code is right in the last Sage.
> But I remain very careful about sum in order to get a1+a2+a3+...+a50.
>
Thanks for clarification and tips :) Just a last doubt: if I
understand correctly, add() wants as argument an array like for
example [1,2,7,5], but running
cos(k*x) for k in [1..n]
alone doesn't return such a thing (it gives error in fact)...
renato
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