MaplePrimes - answers and comments on Question, How do I use plot3d to plot something containing fsolve?

Procedure

Preben Alsholm — Fri, 15 Feb 2013 21:23:39 Z

Although your example is simple, it is a polynomial, so fsolve returns 2 solutions (if they are real).
So I have taken the first one found (the [1] attached to fsolve):
p:=(a,b)->fsolve( x^2 + a*x + b =0, x)[1];
#Use argument free syntax:
plot3d( p , 0.1..5, 0.5..3,axes=boxed,labels=[a,b,p]);

When you don't have a polynomial fsolve only returns one solution, so omit the [1].
Example:

p:=(a,b)->fsolve( x + a*ln(x) + b =0, x);
plot3d( p , 0.1..5, 0.5..3,axes=boxed,labels=[a,b,p]);

Many thank

kolmogorov — Sat, 16 Feb 2013 18:45:24 Z

Many thanks. That worked. It seems that something like

plot3d(p, 0..2, 0..3)

works, while something like

plot3d( p(a,b), a=0..2, b=0..3)

does not.

reference

acer — Sat, 16 Feb 2013 19:27:27 Z

@kolmogorov You might have a look at this page. The error message may not match yours, but it likely covers the same general problem, namely, "when a procedure that requires numeric arguments is called with symbolic arguments."

When you call plot(p(a,b), a=.., b=..) then Maple will try and evaluate p(a,b) for nonnumeric names `a` and `b`. Your procedure `p` may not have been written to deal with symbolic names for those arguments.