optimization/test_functions/extended_powell_gradient1.m

   1 function g = extended_powell_gradient1(x)
   2   ##
   3   ## The gradient of the extended Powell function. See
   4   ## extended_powell1.m for more information.
   5   ##
   6   ## Since the number of arguments is variable, we take a vector
   7   ## instead of its individual components.
   8   ##
   9   n = length(x);
  10
  11   if (odd(n))
  12     ## 'm' below must be an integer.
  13     g = NA;
  14     return;
  15   end
  16
  17   m = n / 4;
  18   g = zeros(n, 1);
  19
  20   % The extended Powell is simply a sum of Powell
  21   % applications.
  22   for k = [ 1 : m ]
  23     y1 = x(4*k - 3);
  24     y2 = x(4*k - 2);
  25     y3 = x(4*k - 1);
  26     y4 = x(4*k);
  27
  28     g_k = powell_gradient(y1, y2, y3, y4);
  29
  30     for i = [ 1 : 4 ]
  31       g(4*(k-1) + i) = g(4*(k-1) + i) + g_k(i);
  32     end
  33
  34   end
  35 end