curve fitting, and finding the parameters

I have this histogram which i need to make a fit by using fminsearch:

I am given this function:

f(x)=Beta*exp(-(x-xc)^2/lambda)

which method would be the best way to use?

[Matt J]

If you must do it by fminsearch, then the method you're to use has been pre-determined.

[Rasmus]

but how do i find the parameters beta, xc and lambda by using it?

[Matt J]

by designing a cost function of the form

    g([beta,xc,lambda]) = norm(f(xi)-measurements)

and minimizing g() with fminsearch.