function value = cubic_fp ( x )

%*****************************************************************************80
%
%% cubic_fp evaluates the derivative of the cubic function.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    21 September 2019
%
%  Input:
%
%    real x, the argument.
%
%  Output:
%
%    real value, the derivative value.
%
  value = 2.0 * x.^2 - 1.0;

  return
end

