Dear Madhusudan,
Very quick reply:
It seems Maxima cannot differentiate with respect to a constant
d and this is reasonable. Therefore, in my opinion, at first the
derivative should be computed and, next, the variable there
should be substituted by the constant d.
Example, for a special function g = u*sin(a*u+b) (the variable is
assumed to be u, the parameters a and b):
(C1) display2d : false$
(C2) h(x) := subst(u=x, diff(u*sin(a*u+b),u))$
(C3) h(d/2);
(D3) SIN(a*d/2+b)+a*d*COS(a*d/2+b)/2
(C4) h(1/2);
(D4) SIN(b+a/2)+a*COS(b+a/2)/2
More generally, for a general function g with a variable u plus,
possibly, parameters such as a and b (or y, z, etc.), assuming
that u appears in g (as its variable) and it is a variable of course:
(C5) f(x,g,u) := subst(u=x, diff(g,u))$
(C6) f(d/2, tanh(a*x^2+b*sin(x)), x);
(D6) (b*COS(d/2)+a*d)*SECH(b*SIN(d/2)+a*d^2/4)^2
(C7) f(1/2, tanh(a*x^2+b*sin(x)), x);
(D7) (COS(1/2)*b+a)*SECH(SIN(1/2)*b+a/4)^2
Best regards from Patras,
Nikos
> "Madhusudan Singh" <chhabra@eecs.umich.edu> wrote:
> Quick question.
>
> How do I calculate the derivative at a point ?
>
> f(x):=diff(g(x),x);
> f(d/2) does not work when d is constant.