function  result_flux_grad_component (i_p)
% Poisson Eq: i_p=1, i_p=2,  i_p=3, i_p=4
%             U,x,x  U,y,x : U,x,y  U,y,y :
% Plane stress: i_p=1, i_p=2, i_p=3,   i_p=4, i_p=5,  i_p=6
%               e_xx,x e_yy,x e_xy,x : e_xx,y e_yy,y, e_xy,y
% or U,x,x V,y,x (U,y + V,x),x : U,x,y V,y,y (U,y + V,x),y
% Copyright 2000, J.E. Akin.  All rights reserved.
%  ------------------------------------------------------
%  Matlab carpet plot of 2-D 2nd deriv i_p-th component value, 
%  at mesh node locations

% The flux gradients are stored as N_R_B flux components
% associated with N_SPACE grident components. Here N_SPACE = 2
% ie N_R_B * N_SPACE options for i_p
%  ------------------------------------------------------

% 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

  fprintf ('Begin component value carpet plots: \n')
  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 pt_ave_grad_flux.tmp
  nr = size (pt_ave_grad_flux, 1);
  if ( nr == 0 )
    error ('Error missing file pt_ave_grad_flux.tmp')
  end % if error
  max_p = size (pt_ave_grad_flux, 2) ; % number of columns
  fprintf ('Read %g nodal solution values \n', nr)
  fprintf ('     with %g components each \n', max_p)
  if ( i_p > max_p ) 
    error ('i_p > available data')
  end % if error

  x (np)      = 0.       ;       % pre-allocate array x
  y (np)      = 0.       ;       % pre-allocate array y
  z (np)      = 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 

  if ( i_p >= 1 )
    z = pt_ave_grad_flux(:, i_p) ;
  else % i_p = 0, get root mean sq
    for k = 1:np
      z (k) = sqrt ( sum (pt_ave_grad_flux (k, 1:max_p).^2)) ;
    end % for k
  end % if get RMS value

%    Cite max, min values
  [V_X, L_X] = max (z) ;
  [V_N, L_N] = min (z) ;
  fprintf ('Max value is %g at node %g \n', V_X, L_X)
  fprintf ('Min value is %g at node %g \n', V_N, L_N)

%    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

%    Get view azimuth and elevation
  [az, el] = view ;

   hold on                           % hold image for plots
   xlabel ('X')                      % add label
   ylabel ('Y')                      % add label
   if ( i_p >= 1 )
     zlabel (['Component ', int2str(i_p), ' (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
     title(['FEA SCP\_ave Component\_', int2str(i_p),': ', ...
            int2str(nt),' Elements, ', int2str(np),' Nodes'])
   else % i_p = 0, get root mean sq
     zlabel (['RMS Value (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
     title(['FEA XXXXXxxx RMS Value: ', ...
            int2str(nt),' Elements, ', int2str(np),' Nodes'])
   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
    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
    c_z  = t_z (loop) ;
    plot3 (c_x, c_y, c_z)           % plot nod_per_el lines
  end % for over all elements
  plot3(c_x, c_y, c_z), grid      % add grid to last one
 
% label max min points 
  % plot3 (x(L_X), y(L_X), V_X, 'kx')
  % plot3 (x(L_N), y(L_N), V_N, 'ko')
  v_text = sprintf ('------min') ;
  text  (x(L_N), y(L_N), V_N, v_text) ;
  v_text = sprintf ('------max') ;
  text  (x(L_X), y(L_X), V_X, [v_text]) ;   ;

% end % if show labels
%       -depsc -tiff            % for an eps version
  print ('-dpsc', ['flux_grad_component_', int2str(i_p)])
  hold off
  v_text = ['Created flux_grad_component_', int2str(i_p),'.ps'] ;
  fprintf (1,'%s', v_text) ; fprintf (1, ' \n' )
% end of result_flux_grad_component