function un = shock_wave ( x )

%*****************************************************************************80
%
%% shock_wave evaluates a shock wave.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    03 June 2020
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real X(*), the node coordinates.
%
%  Output:
%
%    real UN(*), the value of the initial condition at each node.
%
  un = 0.1 + 0.9 * ( x <= 0.0 );

  return
end
