function value = r8_sigmoid ( x )

%*****************************************************************************80
%
%% R8_SIGMOID evaluates the sigmoid function.
%
%  Discussion:
%
%    An R8 is a double precision real value.
%
%    The sigmoid function is useful for classification problems in
%    machine learning.  Its value is always between 0 and 1.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    27 August 2018
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, real X, the argument.
%
%    Output, real VALUE, the value.
%
  value = 1.0 ./ ( 1.0 + exp ( - x ) );

  return
end

