function value = runge_fun ( x )

%*****************************************************************************80
%
%% runge_fun() evaluates the Runge function.
%
%  Discussion:
%
%    This function causes a breakdown for
%    polynomial interpolation over equally spaced nodes in [-1,+1].
%
%    Runge originally considered the function 1/(1+x^2) over the
%    interval [-5,+5].  For convenience, a rescaled version is considered
%    over the interval [-1,+1].
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    24 March 2025
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real x: the argument of the function.
%
%  Output:
%
%    real value: the value of the function.
%
  value = 1.0 ./ ( 1.0 + 25.0 * x .* x );

  return
end
