Solve Equation with symbolic Constants numerically.

Say I have got the Planck's law whose maximum I want to determine numerically:

% a = hbar/(pi^2*c^3)

% b = hbar./(kB*T); 

syms w a b positive real; u = a * w^3/(exp(b*w)-1);

du = diff(u,w);

How can I numerically solve du for w but leaving constants a and b?

I tried many solvers like

fzero(matlabFunction(du),w)

But all of these accept constants in the form of double inputs only.

Is there a way to get a result with Constants included? Like:

w = 2.82 * b % this is in fact the standard result. 

Answer 1

[Torsten]

syms w a b positive real
u = a * w^3/(exp(b*w)-1);
du = diff(u,w);
wsol = solve(du==0,w)

wsol =