function retval = exerfnhess(x)
% usage: hess = exerfnhess(x)
% description: Returns the Hessian matrix for
% exerfn(x). It is *assumed* that length(x) is even!

% for adapting this problem, use c
c = 10;
m = length(x);
retval = zeros(m,m);
for j = (1:2:m)
  retval(j:j+1,j:j+1) = [2-4*c*x(j+1)+12*c*x(j)^2, -4*c*x(j); -4*c*x(j) 2*c];
end