function  ex_error_value_plot ()
% Copyright 2000, J.E. Akin.  All rights reserved.
%  ------------------------------------------------------
%  Matlab plot 2-D FE exact numerical error in elements
%  ------------------------------------------------------

% c_x    = x coordinates of nod_per_el line polygon
% c_y    = y coordinates of nod_per_el line polygon
% inc_e  = increment in element %-error on plot, if > 0
  inc_e  = 1 ;
% inc_p  = increment in node numbers on plot, if > 0
% msh_typ_nodes   = connectivity list for elements, nt x nod_per_el
% loop   = corners for nod_per_el line polygon
% lab_p  = 1, if node points are circled
  lab_p  = 0;
% nod_per_el = Nodes per element
% np     = Number of Points
% nt     = Number of elements
% pre_e  = Element items before connectivity list
  pre_e  = 0 ;
% pre_p  = Nodal items before coordinates
  pre_p = 1;
% msh_bc_xyz = Nodal coordinates (with preceeding data)
% t_x    = x coordinates of nod_per_el corners
% t_y    = y coordinates of nod_per_el corners
% x_bar  = x-centroid of each element
% xy     = Coordinates of points, np x 2
% y_bar  = y-centroid of each element

  fprintf ('\n Begin element error value plots: \n')

%    Read coordinate file and connectivity file
%    integer bc code, real xy pairs for np points (pre_p = 1)

%    Set control data: number of points
  load msh_bc_xyz.tmp ;  
  np = size (msh_bc_xyz,1) ;   % number of nodal points  
  ns = size (msh_bc_xyz,2) - pre_p ;   % dimension of space
  if ( np == 0 )
    error ('Error missing file msh_bc_xyz.tmp')
  end % if error
  fprintf ('\n Read %g mesh coordinate pairs \n', np)
  % fprintf ('       x        y \n')
  
%    Set control data: number elements & nodes per element
  load  msh_typ_nodes.tmp ; % nod_per_el nodes per element
  nt = size (msh_typ_nodes,1) ;          % number of elements in mesh 
  nod_per_el = size (msh_typ_nodes,2) - pre_e -1 ; % nodes per element
  fprintf ('\n Read %g elements connections \n', nt)
% fprintf ('Pt1    Pt2    Pt3    Pt4    Pt5    Pt6    Pt7    Pt8 \n')

  load ex_error_est.tmp
  nerr = size (ex_error_est,1) ;
  if ( nerr == 0 )
    error ('Error missing file ex_error_est.tmp')
  end % if error
  fprintf ('\n Read %g elements error values \n', nerr)
  [V_X, L_X] = max (ex_error_est) ;
  [V_N, L_N] = min (ex_error_est) ;
  V_XN = V_X - V_N + eps; % for color scale
  fprintf ('Max value is %g in element %g \n', V_X, L_X)
  fprintf ('Min value is %g in element %g \n', V_N, L_N)

  x (np)      = 0.       ;       % pre-allocate array x
  y (np)      = 0.       ;       % pre-allocate array y
  x_bar (nt)  = 0.       ;       % pre-allocate array x_bar
  y_bar (nt)  = 0.       ;       % pre-allocate array y_bar
  t_nodes (nod_per_el) = 0 ;    % Optional pre-allocation
  t_x (nod_per_el) = 0 ;        % Optional pre-allocation
  t_y (nod_per_el) = 0 ;        % Optional pre-allocation
  c_x (nod_per_el + 1) = 0 ;    % Optional pre-allocation
  c_y (nod_per_el + 1) = 0 ;    % Optional pre-allocation
  loop (nod_per_el + 1) = 0 ;   % Optional pre-allocation

%                set constants
  [loop] = get_El_Loop (nod_per_el) ;

  % msh_bc_xyz has: pre_p items then: x, y
  x = msh_bc_xyz (1:np, (pre_p+1)) ; % extract x column of xy
  if ( ns >= 2)
    y = msh_bc_xyz (1:np, (pre_p+2)) ; % extract y column of xy
  else
    y (1:np) = 0. ;
  end % if 1D
 
%    Initialize plots
  xmax = max (x)      ; xmin = min (x) ;
  ymax = max (y)      ; ymin = min (y) ;
  xdiff = xmax - xmin ; ydiff = ymax - ymin ;
  if ( ns == 1 )
  % if ( ydiff == 0.0 )
    % ydiff = 0.5 ; % allow for 1-D mesh (with y == 0)
    ydiff = xdiff/10 ; % allow for 1-D mesh (with y == 0)
  end % if no y coordinates
  xmax = xmax + xdiff/10; ymax = ymax + ydiff/10;
  xmin = xmin - xdiff/10; ymin = ymin - ydiff/10;
  clf                               % clear graphics
  axis ([xmin, xmax, ymin, ymax])   % set axes
  axis ('equal')                    % true shape style
  hold on                           % hold image for plots
  grid                              % add grid dots
  % xlabel ('X') ; ylabel ('Y')                      % add label
  xlabel (['X: ', int2str(nt),' Elements'])
  ylabel (['Y: ', int2str(np),' Nodes'])
 title('Exact FEA Element Error Values, % Energy\_norm * 100')
 
%      Plot input mesh points 
  if (lab_p == 1)                   % plot all points
    plot (x, y, 'b.')               % mark each node
  end % if show labels

%    Show 20 nodes and 50 elements
  inc_p = floor(np/20) ; inc_e = floor(nt/50) ;
  if (inc_p == 0 ) 
    inc_p = np - 1 ;
  end % if inc_p
  if (inc_e == 0 ) 
    inc_e = nt - 1 ;
  end % if inc_e
%    Show all if a small mesh
  if ( np <= 20 )
    inc_p = 1 ;
  end % if np
  if ( nt <= 50 )
    inc_e = 1 ;
  end % if nt

  if (inc_p > 0)                      % plot node numbers
    for i = 1:inc_p:np                % convert to string
      p_text = sprintf ('  %g', i);   % offset # from pt
      text (x(i), y(i), p_text)       % plot pt number
    end % for all points
  end % if show labels
  disp (' ')

%    Loop over all elements
  for it = 1:nt  ;

%      Extract corner connectivity 
    t_nodes = msh_typ_nodes (it, (pre_e+2):(nod_per_el+pre_e+1)); 

%      Extract corner coordinates
    t_x  = x (t_nodes) ;         % x at those nodes, only
    t_y  = y (t_nodes) ;         % y at those nodes, only

%      Get the centroid
    x_bar (it) = sum (t_x' )/nod_per_el ;
    y_bar (it) = sum (t_y' )/nod_per_el ;

%      Plot this polygon
    c_x  = t_x (loop) ;       % x for nod_per_el line polygon
    c_y  = t_y (loop) ;       % y for nod_per_el line polygon
    plot (c_x, c_y,'b-')           % plot nod_per_el lines in blue
  end % for over all elements

%      Show max & min element value 
   if ( ns > 1 )
     p_text = sprintf ('*---MIN %6.1f', V_N*100);     % offset # from pt
     text (x_bar(L_N), y_bar(L_N), p_text)   % plot min value
     p_text = sprintf ('*---MAX %6.1f', V_X*100);     % offset # from pt
     text (x_bar(L_X), y_bar(L_X), p_text)   % plot max value
   end % if 2-D
 
%    Finish the plots with elem error estimate numbers
  if (inc_e > 0)                     % plot elem number, inclined
    for i = 1:inc_e:nt               % convert to string
      v = 100. * ex_error_est (i) ;  % el %-error value
      t_text = sprintf ('%g', v);    % convert to text  
      text (x_bar(i), y_bar(i), t_text, 'Rotation', 40) % incline
    end % for all polygons
  end % if show labels
%       -depsc -tiff            % for an eps version
  %bprint -dpsc ex_error_value_plot
  hold off
%bfprintf ('Created file ex_error_value_plot.ps \n')
% end of ex_error_value_plot