Creating a gradient ascent matlab function?

I have to create a gradient ascent matlab function to find the maximum of a function. The inputs are a function handle, an initial guess, which is a 2 by 1 vector, a maximum number of iterations, and a convergence tolerance.

This is the function I'm testing it on:

    function test=funcl(x0)
        test=x0(1)^3-7*x0(1)^2+4*x0(1)+9*x0(2)-2*x0(2)^2;
    end

It has to call a function called gs_max, which finds the maximum of a function between a lower and upper bound using the golden section method.

This is what I have so far:

    function [x,fval,exitFlag]=gradient_ascent_2D(fhandle,x0,TolX,MaxIter)
    for ii=1:MaxIter
        if x0(1)<.000001
           dx(1)=(feval(fhandle,x0(1)+x0(1)+.000001)-feval(fhandle,x0(1)))/.000001
        else
           dx(1)=(feval(fhandle,x0(1)+x0(1)*.000001)-feval(fhandle,x0(1)))/.000001
        end

        if x0(2)<.000001
            dx(2)=(feval(fhandle,x0(2)+x0(2)+.000001)-feval(fhandle,x0(2)))/.000001
        else
            dx(2)=(feval(fhandle,x0(2)+x0(2)*.000001)-feval(fhandle,x0(2)))/.000001
        end

    xnew(:)=x0(:)+dx(:)
    xmax=gs_max(fhandle,x0(:),xnew

When I run this, I get an error that says:

    Attempted to access x0(2); index out of bounds because numel(x0)=1.

    Error in funcl (line 2)
    test=x0(1)^3-7*x0(1)^2+4*x0(1)+9*x0(2)-2*x0(2)^2;

    Error in gradient_ascent_2D (line 48)
            dx(1)=(feval(fhandle,x0(1)+x0(1)*.000001)-feval(fhandle,x0(1)))/.000001

I don't understand why I'm getting this error and no matter what I try I cant get it to go away. Even if I figured this out, my function still won't be right, and I don't know where to go from here. Any ideas?

[per isakson]

Here are some links on debugging in Matlab

• Debugging in MATLAB
• Debugging session
• Debugging Approaches