function f = rosenbrock(x1, x2)
  ##
  ## The Rosenbrock function. See Dennis & Schnabel, Appendix B, problem #1.
  ## (The "regular" Rosenbrock function is simply the Extended Rosenbrock
  ## with m=1).
  ##
  ## This function has a minimum at x=(1,1) with f(x) == 0. The
  ## suggested starting point is x0=(-1.2, 1).
  ##
  f = 100*(x2 - x1^2)^2 + (1 - x1)^2;
end
