function lagrange_approx_1d_test01 ( prob, m )

%*****************************************************************************80
%
%% lagrange_approx_1d_test01() tests lagrange_approx_1d().
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    14 August 2012
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    integer PROB, the problem index.
%
%    integer M, the polynomial approximant degree.
%
  fprintf ( 1, '\n' );
  fprintf ( 1, 'lagrange_approx_1d_test01():\n' );
  fprintf ( 1, '  Approximate data from test_interp() problem #%d.\n', prob );
  fprintf ( 1, '  Use polynomial approximant of degree %d.', m );

  nd = p00_data_num ( prob );
  fprintf ( 1, '  Number of data points = %d\n', nd );

  xy = p00_data ( prob, 2, nd );
  
  if ( nd < 10 )
    fprintf ( 1, '\n' );
    fprintf ( 1, '  Data array:' );
    disp ( xy' );
  end

  xd = reshape ( xy(1,1:nd), nd, 1 );
  yd = reshape ( xy(2,1:nd), nd, 1 );
%
%  #1:  Does approximant come close to function at data points?
%
  ni = nd;
  xi = xd;
  yi = lagrange_approx_1d ( m, nd, xd, yd, ni, xi );

  int_error = norm ( yi - yd ) / ni;

  fprintf ( 1, '\n' );
  fprintf ( 1, '  L2 approximation error averaged per data node = %g\n', int_error );
%
%  #2: Compare estimated curve length to piecewise linear (minimal) curve length.
%  Assume data is sorted, and normalize X and Y dimensions by (XMAX-XMIN) and
%  (YMAX-YMIN).
%
  xmin = min ( xd(1:nd) );
  xmax = max ( xd(1:nd) );
  ymin = min ( yd(1:nd) );
  ymax = max ( yd(1:nd) );

  ni = 501;
  xi = linspace ( xmin, xmax, ni );
  yi = lagrange_approx_1d ( m, nd, xd, yd, ni, xi );

  ld = sum ( sqrt ( ( ( xd(2:nd) - xd(1:nd-1) ) / ( xmax - xmin ) ).^2 ...
                  + ( ( yd(2:nd) - yd(1:nd-1) ) / ( ymax - ymin ) ).^2 ) );

  li = sum ( sqrt ( ( ( xi(2:ni) - xi(1:ni-1) ) / ( xmax - xmin ) ).^2 ...
                  + ( ( yi(2:ni) - yi(1:ni-1) ) / ( ymax - ymin ) ).^2 ) );

  fprintf ( 1, '\n' );
  fprintf ( 1, '  Normalized length of piecewise linear interpolant = %g\n', ld );
  fprintf ( 1, '  Normalized length of polynomial interpolant       = %g\n', li );
%
%  #3: Plot the piecewise linear interpolant and polynomial approximant.
%
  figure ( 1 );
  clf ( );
  ni = 101;
  xmin = min ( xd );
  xmax = max ( xd );
  xi = linspace ( xmin, xmax, ni );
  yi = lagrange_approx_1d ( m, nd, xd, yd, ni, xi );

  hold ( 'on' );
  plot ( xd, yd, 'k.', 'Markersize', 30 );
  plot ( xi, yi, 'r-', 'Linewidth', 3 );
  plot ( xd, yd, 'b-', 'Linewidth', 3 );
  xlabel ( '<--- X --->' );
  ylabel ( '<--- Y --->' );
  title ( sprintf ( 'Lagrange Polynomial Approximant of Degree %d', m ) );
  grid ( 'on' );
  hold ( 'off' );

  filename = sprintf ( 'p%02d_approx_%02d.png', prob, m );
  print ( '-dpng', filename );
  fprintf ( 1, '  Graphics saved as "%s".\n', filename );

  return
end
