function f1 = p13_f1 ( x )

%*****************************************************************************80
%
%% p13_f1() evaluates the first derivative for problem 13.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    02 August 2019
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real x, the value of the variable.
%
%  Output:
%
%    real f1, the first derivative of the objective function.
%
  f1 = 8.0 * x.^3 - 14.0 * x + 3.0;

  return
end
