function exercise7task2

f = @(x,y) x.*y.*exp(x.*y);

h = 1./2.^(1:20);
D2f = zeros(1,length(h));

for k = 1:length(h)
    D2f(k) = ( 1/6*(f(1+h(k),1+h(k))+f(1+h(k),1-h(k))+f(1-h(k),1+h(k))+f(1-h(k),1-h(k))) + 2/3*(f(1+h(k),1)+f(1-h(k),1)+f(1,1+h(k))+f(1,1-h(k))) - 10/3*f(1,1) )/h(k)^2;
end

loglog(h,abs(D2f-6*exp(1)))