Subst is purely syntactic. Probably a bad design, but there it is. Try
"at".
-s
On Tue, Jun 26, 2012 at 2:54 AM, J?rome Laurens <
jerome.laurens at u-bourgogne.fr> wrote:
> Hi list,
>
> here is the problem
>
> (%i1) integrate('diff(f(t)*diff(g(t),t),t),t,0,1);
> d d
> (%o1) limit f(t) (-- (g(t))) - limit f(t) (-- (g(t)))
> t -> 1- dt t -> 0+ dt
> (%i2)
> assume(alpha>0);integrate('diff(f(t)*diff(g(t),t),t),t,0,sqrt(alpha));
> (%o2) [alpha > 0]
> d d
> (%o3) limit f(t) (-- (g(t))) - limit f(t) (-- (g(t)))
> t -> sqrt(alpha)- dt t -> 0+ dt
> (%i4)
> assume(beta>0);integrate('diff(f(t)*diff(g(t),t),t),t,sqrt(beta),sqrt(alpha));
> (%o4) [beta > 0]
> d
> (%o5) (------------ (g(sqrt(alpha)))) f(sqrt(alpha))
> dsqrt(alpha)
> d
> - (----------- (g(sqrt(beta))))
> f(sqrt(beta))
> dsqrt(beta)
> (%i6) subst(0,alpha,%);
>
> diff: variable must not be a number; found: 0
> -- an error. To debug this try: debugmode(true);
> (%i7) diff(g(sqrt(beta)),sqrt(beta));
>
> diff: second argument must be a variable; found sqrt(beta)
> -- an error. To debug this try: debugmode(true);
>
> That is both inconsistent and far from nice!
>
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>