function retval = extrosenfn(x)
% usage:  y = extrosenfn(x)
% description: Returns value of function of function 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 hessian functions.

c = 10;
m = length(x);
retval = sum((1-x(1:2:m-1)).^2 + c*(x(2:2:m)-x(1:2:m-1).^2).^2);