You should change the definition of g(x) to g(x):=''(diff(f(x), x))
(parenthesis are important).
Andrej
On 7/20/07, Moby <maxima at mobsternet.com> wrote:
> After much googling and ogling various web sites, I believe I have
> stumbled on a bug in Maxima having to do with evaluating functions that
> are derivatives of other functions for given values of the independent
> variable.
>
> Consider:
>
> (%i1) f(x):=sin(x);
> (%o1) f(x):=sin(x)
> (%i2) f(%pi);
> (%o2) 0
> (%i3) f(4*%pi);
> (%o3) 0
> (%i4) g(x):='' diff(f(x),x);
> (%o4) g(x):=diff(f(x),x)
> (%i5) g(x);
> (%o5) cos(x)
> (%i6) g(%pi);
> (%o6) 0
> (%i7) g(4*%pi);
> Non-variable 2nd argument to diff:
> 4*%pi
> #0: g(x=4*%pi)
> -- an error. To debug this try debugmode(true);
>
> I am not sure why g(%pi) evaluates fine, but g(4*%pi) does not. I know
> my syntax for specifying 4 pi is correct, since the same works for
> evaluating f(x) at 4 pi.
>
> Any help in determining why this does not work, and how to get it work,
> would be much appreciated.
>
> --Moby
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