function p20_demo ( iteration_max, h )

%*****************************************************************************80
%
%% P20_DEMO runs the 2D demo problem #20, with mesh size H.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    26 April 2012
%
%  Author:
%
%    John Burkardt
%
%  Reference:
%
%    Per-Olof Persson, Gilbert Strang,
%    A Simple Mesh Generator in MATLAB,
%    SIAM Review,
%    Volume 46, Number 2, June 2004, pages 329-345.
%
%  Parameters:
%
%    Input, integer ITERATION_MAX, the maximum number of iterations. 
%
%    Input, real H, the mesh spacing parameter.
%
  if ( nargin < 1 )
    iteration_max = 2;
    fprintf ( 1, '\n' );
    fprintf ( 1, 'P20_DEMO - Note:\n' );
    fprintf ( 1, '  No value of ITERATION_MAX was supplied.\n' );
    fprintf ( 1, '  The default value ITERATION_MAX = %d will be used.\n', ...
      iteration_max );
  end

  if ( nargin < 2 )
    h = 2.0;
    fprintf ( 1, '\n' );
    fprintf ( 1, 'P20_DEMO - Note:\n' );
    fprintf ( 1, '  No value of H was supplied.\n' );
    fprintf ( 1, '  The default value H = %f will be used.\n', h );
  end
%
%  Choose the uniform or nonuniform mesh option.
%
  uniform = 1;
%
%  Put the random number generator into a fixed initial state.
%
  rand ( 'state', 111 );
%
%  Set the rendering method for the current figure to Z-buffering.
%
  set ( gcf, 'rend', 'z' );

  fprintf ( 1, '\n' );
  fprintf ( 1, 'Problem 20:\n' );
  fprintf ( 1, '  ICAM / Wright House, h = %f\n', h )
  if ( uniform )
    fprintf ( 1, '  UNIFORM mesh spacing requested.\n' );
  else
    fprintf ( 1, '  NONUNIFORM mesh spacing requested.\n' );
  end

  fd = @p20_fd;

  if ( uniform) 
    fh = @p20_uniform_fh;
  else
    fh = @p20_nonuniform_fh;
  end

  box = [ 0.00, 0.00; 41.00, 98.00 ];

  fixed = [ ...
     7.25,  0.25; ... % Lower left corner of R1.
    14.75,  0.25; ...
    14.75,  7.75; ...
    13.00,  7.75; ...
    13.00,  8.25; ...
    25.00,  8.25; ...
    25.00,  7.75; ...
    15.25,  7.75; ...
    15.25,  0.25; ... % Lower left corner of R2.
    28.75,  0.25; ...
    28.75,  7.75; ...
    28.75,  8.25; ...
    29.25,  8.25; ...
    29.25,  7.75; ...
    29.25,  0.25; ... % Lower left corner of R3.
    40.75,  0.25; ...
    40.75,  7.75; ...
    33.00,  7.75; ...
    33.00,  8.25; ...
    33.25,  8.25; ... % Lower left corner of R5.
    40.75,  8.25; ...
    40.75, 17.75; ...
    33.25, 17.75; ...
    33.25, 12.00; ... 
    32.75, 12.00; ...
    32.75, 21.75; ...
    20.75, 21.75; ...
    20.75, 22.25; ...
    21.25, 22.25; ... % Lower left corner of R8.
    32.75, 22.25; ...
    32.75, 25.25; ...
    35.75, 25.25; ...
    35.75, 34.75; ...
    32.75, 34.75; ...
    32.75, 37.75; ...
    21.25, 37.75; ...
    21.25, 26.00; ...
    20.75, 26.00; ...
    20.75, 38.25; ...
    25.75, 38.25; ...
    26.25, 38.25; ... % Lower left corner of R11.
    32.75, 38.25; ...
    32.75, 45.75; ...
    26.25, 45.75; ...
    26.25, 41.75; ...
    25.75, 41.75; ...
    25.75, 46.25; ...
    26.25, 46.25; ... % Lower left corner of R15.
    32.75, 46.25; ...
    32.75, 53.75; ...
    26.25, 53.75; ...
    26.25, 49.25; ...
    25.75, 49.25; ...
    25.75, 53.75; ...
    23.75, 53.75; ...
    23.75, 62.75; ...
    23.75, 97.75; ...
    16.25, 97.25; ...
    16.25, 88.00; ...
    15.75, 88.00; ...
    15.75, 97.25; ...
     0.25, 97.25; ...
     0.25, 75.25; ... % Lower left corner of R21
    15.75, 75.25; ...
    15.75, 85.00; ...
    16.25, 85.00; ...
    16.25, 74.75; ...
     0.25, 74.75; ...
     0.25, 63.25; ... % Lower left corner of R19
    16.25, 63.25; ...       
    16.25, 62.75; ...
    16.25, 58.25; ... % Lower left corner of R18
    19.25, 58.25; ...
    19.25, 54.25; ...
    20.25, 54.25; ...
    20.25, 53.75; ...
    20.25, 50.75; ... % Lower left corner of R16.
    23.25, 50.75; ...
    23.25, 41.75; ...
    17.25, 41.75; ...
    16.75, 41.75; ...
    16.75, 53.75; ...
     7.25, 53.75; ...
     7.25, 38.25; ...
    17.25, 38.25; ... 
    17.25, 37.75; ...
     7.25, 37.75; ...
     7.25, 22.25; ...
    16.75, 22.25; ...
    16.75, 34.25; ...
    17.25, 34.25; ...
    17.25, 21.75; ...
     7.25, 21.75; ...
     7.25,  8.25; ... % Lower left corner of R4.
     9.00,  8.25; ...
     9.00,  7.75; ...
     7.25,  7.75 ];

  [ p, t ] = distmesh_2d ( fd, fh, h, box, iteration_max, fixed );

  if ( 0 )
    post_2d ( p, t, fh )
  end
%
%  Write the nodes and triangles of the mesh to a file.
%
  if ( 1 )

    [ node_num, junk ] = size ( p );
    [ tri_num, junk ] = size ( t );

    if ( uniform )
      r8mat_write ( 'p20_uniform_nodes.txt', 2, node_num, p' );
      i4mat_write ( 'p20_uniform_elements.txt', 3, tri_num, t' );
    else
      r8mat_write ( 'p20_nonuniform_nodes.txt', 2, node_num, p' );
      i4mat_write ( 'p20_nonuniform_elements.txt', 3, tri_num, t' );
    end

  end

  return
end