If you want to call a function file you have to create a function handle for it with the ‘@’ operator. In the situation you illustrated, you would call it as
q = quad(@fun,a,b);
That said, do not call your function from inside your function! It would have created recursion problems even if it would have worked. (It wouldn’t have, because quad wants two limits for its integration, not a vector.)
So simply use quad with an anonymous function expression for your function, and your limits:
y= @(x) x.^3-2*x.^2-5*x+6; % Anonymous Function
q=quad(y, -4, 4); % Integrate
producing a value for ‘q’ of about -37.3.
