function yp = p06_fun ( neqn, t, y )

%*****************************************************************************80
%
%% P06_FUN evaluates the function for problem P06.
%
%  Discussion:
%
%    y1' = 2 y1 * ( 1 - y2 )
%    y2' = - y2 * ( 1 - y1 )
%    y1(0) = 1
%    y2(0) = 3
%
%    2 equations.
%    Enright and Pryce nonstiff problem #B1.
%    Autonomous.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    17 February 2013
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Wayne Enright, John Pryce,
%    Algorithm 648,
%    ACM Transactions on Mathematical Software,
%    Volume 13, Number 1, pages 28-34.
%
%  Parameters:
%
%    Input, integer NEQN, the number of equations.
%
%    Input, real T, Y(NEQN), the arguments of the derivative
%    function.
%
%    Output, real YP(NEQN), the value of the derivative function.
%
  yp = zeros ( neqn, 1 );

  yp(1) = 2.0 * y(1) * ( 1.0 - y(2) );
  yp(2) =     - y(2) * ( 1.0 - y(1) );

  return
end
