optimization/test_functions/powell_gradient.m

   1 function g = powell_gradient(x1,x2,x3,x4)
   2   ##
   3   ## The gradient of the Powell function. See powell.m for more
   4   ## information.
   5   ##
   6   f_x1 = 40*(x1 - x4)^3 + 2*x1 + 20*x2;
   7   f_x2 = 4*(x2 - 2*x3)^3 + 20*x1 + 200*x2;
   8   f_x3 = -8*(x2 - 2*x3)^3 + 10*x3 - 10*x4;
   9   f_x4 = -40*(x1 - x4)^3 - 10*x3 + 10*x4;
  10
  11   g = [f_x1; f_x2; f_x3; f_x4];
  12 end