a function of function problem

I have an expression f in terms of y (independent variable), a and b(parameters). I would like to take the derivative of f with respect to y, and then set the first order condition df/dy=0 to solve for y. The codes are

function g=derive(y,a,b)
g=diff(fun,y);
end;

function [f,c1,c2]=fun(y,a,b)
f=a*log(c1)+b*log(c2);
c1=y*a;
c2=y*b;
end

y0=1;
y_max=fsolve(g,y0);

I know there are problems in the code. The logic is clear, and I hope someone can tell me how to use function of function (local function or nested function) to solve this problem.

Answer 1

[Walter Roberson]

Your code will fail at the diff() if y is not symbolic, unless y happens to be 1.

If y is symbolic, then you need to use solve() with g instead of using fsolve() .

Remember to assign a value to g before calling the solving routine. See http://www.mathworks.com/matlabcentral/answers/281617-i-am-having-some-issues-calling-a-function-in-a-script-file#answer_219973