function cdf = folded_normal_cdf ( x, a, b )

%*****************************************************************************80
%
%% FOLDED_NORMAL_CDF evaluates the Folded Normal CDF.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    11 September 2004
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, real X, the argument of the CDF.
%    0.0 <= X.
%
%    Input, real A, B, the parameters of the PDF.
%    0.0 <= A,
%    0.0 < B.
%
%    Output, real CDF, the value of the CDF.
%
  if ( x < 0.0 )
    cdf = 0.0;
  else
    x1 = ( x - a ) / b;
    cdf1 = normal_01_cdf ( x1 );
    x2 = ( - x - a ) / b;
    cdf2 = normal_01_cdf ( x2 );
    cdf = cdf1 - cdf2;
  end

  return
end