function retval = extrosenfnhess(x)
% usage: hess = extrosenfnhess(x)
% description: Returns the Hessian matrix for extrosenfn
% of Exercise 9.1 of Nocedal and Wright's text, Numerical
% Optimization.  This is the extended Rosenbrock
% function. It is *assumed* that length(x) is even!
% Solution is x* = (1,1,...,1), minimum value 0.

% no bulletproofing
% for adapting this problem, change c here and in
% gradient and original functions.

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