function  color_qp_fluxes (i_p)
% UNDER CONSTRUCTION
% i_p = flux component or 0 for RMS value
% Copyright 2000, J.E. Akin.  All rights reserved.
%  ------------------------------------------------------
%  Matlab color plot of i_p-th component value, 
%  at mesh  quadrature point locations
%  ------------------------------------------------------

% c_x    = x coordinates of nod_per_el line polygon
% c_y    = y coordinates of nod_per_el line polygon
% msh_typ_nodes   = connectivity list for elements, nt x nod_per_el
% loop   = corners for nod_per_el line polygon
% 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

format short g
  if ( nargin == 0 )
    i_p = 0 ;
  end % if no arguments

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

%    Set control data: number of points
  np = size (msh_bc_xyz,1) ;   % number of nodal points  
  fprintf ('Read %g mesh coordinate pairs \n', np)
  ns = size (msh_bc_xyz,2) - pre_p ;   % space dimension
  if ( ns < 2 )
    error ('This is not a 2D mesh')
  end % if not 2D data
  
%    Set control data: number elements
  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 elem
  fprintf ('Read %g elements connections \n', nt)

  load el_qp_xyz_fluxes.tmp
  nr = size (el_qp_xyz_fluxes, 1);
  if ( nr == 0 )
    error ('Error missing file el_qp_xyz_fluxes.tmp')
  end % if error
  %b if ( nr ~= 4*nt )
    %b error 'Script set for 4 Gauss points per element'
  %b end % if
  max_p = size (el_qp_xyz_fluxes, 2) ; % number of columns
  fprintf ('Read %g qp flux values \n', nr)
  fprintf ('     with %g components each \n', max_p)
  nr = nr / nt ;
  if ( i_p > (max_p+1) ) 
    error ('i_p > available data')
  end % if error

  x (np)      = 0.       ;       % pre-allocate array x
  y (np)      = 0.       ;       % pre-allocate array y
  z (nt)      = 0.       ;       % pre-allocate array z
  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
  y = msh_bc_xyz (1:np, (pre_p+2)) ; % extract y column 

  root_2 = sqrt (2.) ;

%    average element value for color
  for it = 1:nt
    %b here = 4*(it-1) + 1;
    here = nr*(it-1) + 1;
    last = here + nr - 1;
    if ( i_p > 0 )
      z (it) = mean ( el_qp_xyz_fluxes(here:last, i_p+2) ) ;
    else % use RMS
      xxxx
    end % if
  end % for

%    Cite max, min values
  [V_X, L_X] = max (z) ;
  [V_N, L_N] = min (z) ;
  fprintf ('Max value is %g at element %g \n', V_X, L_X)
  fprintf ('Min value is %g at element %g \n', V_N, L_N)
  if ( V_X == V_N ) % constant value plot, trick colors
    caxis([V_N (V_X + 1)]) ; % set full color ranges
  else
    caxis([V_N V_X]) ; % set full color ranges
  end % if

%    Initialize plots
   xmax = max (x)      ; xmin = min (x) ;
   ymax = max (y)      ; ymin = min (y) ;
%  zmax = max (z)      ; zmin = min (z) ;
   clf                               % clear graphics
%  axis ([xmin, xmax, ymin, ymax, zmin, zmax])   % set axes
   axis ([xmin, xmax, ymin, ymax])   % set axes
   %b axis ('square')
axis('equal')

   hold on                           % hold image for plots
   xlabel (['X at ', int2str(np),' Nodes'])           
   ylabel (['Y on ', int2str(nt),' Elements (with ', ...
            int2str(nod_per_el), ' nodes) '])
format short g
   if ( i_p == 0 )
     title(['             Flux RMS values (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
   else
     title(['             Flux component ', int2str(i_p),' (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
   end % if get RMS value

%    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
    %XXX t_z  = z (t_nodes) ;         % z at those nodes, only

%      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
    %XXX c_z  = t_z (loop) ;
    color = z(it) ;
    fill (c_x, c_y, color)           % plot nod_per_el lines
  end % for over all elements
  fill (c_x, c_y, color), grid      % add grid to last one
  colorbar
 
% end % if show labels
%       -depsc -tiff            % for an eps version
  %bprint ('-dpsc', ['color_stresses_', int2str(i_p), '_step'])
  hold off
  %bv_text = ['Created color_stresses_', int2str(i_p), '_step.ps'] ;
  %bfprintf (1,'%s', v_text) ; fprintf (1, ' \n' )
% end of color_qp_fluxes