function exact = p31_exact ( )

%*****************************************************************************80
%
%% p31_exact() returns the exact integral for problem 31.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    04 November 2009
%
%  Author:
%
%    John Burkardt
%
%  Output:
%
%    real EXACT, the value of the integral.
%
  exact = 2.0 * atan ( 4.0 );

  return
end
