First make a function that you'll use to fit like this:
function val = myfunc(par_fit,x,y)
% par_fit = [a b]
val = norm(y - par_fit(1)*exp(x.^2-2^par_fit(2)));
Now, find the parameters like:
my_par = fminsearch(@(par_fit) myfunc(par_fit,x,y),rand(1,2));
