function f = extended_rosenbrock ( x )

%% EXTENDED_ROSENBROCK computes the extended Rosenbrock function.
%
%  Discussion:
%
%    The number of dimensions is arbitrary, except that it must be even.
%
%    There is a global minimum at X* = (1,1,...), F(X*) = 0.
%
%    The contours are sharply twisted.
%
%  Modified:
%
%    26 January 2008
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Howard Rosenbrock,
%    An Automatic Method for Finding the Greatest or Least Value of a Function,
%    Computer Journal,
%    Volume 3, 1960, pages 175-184.
%
%  Parameters:
%
%    Input, real X(N), the argument of the function.
%
%    Output, real F, the value of the function at X.
%
  [ n, dim ] = size ( x );

  if ( mod(dim,2) ~= 0 )
    error  (  'Extended Rosenbrock function expects an even-dimensional input.\n' );
  end

  r = zeros ( dim, 1 );

  for i=1:dim/2
    r(2*i-1) = 1 - x(2*i-1);
    r(2*i  ) = 10 * ( x(2*i) - x(2*i-1)^2 );
  end

  f = r' * r;