function  flux_on_const_y (i_p, y_p)
% Copyright 2000, J.E. Akin.  All rights reserved.
%  ------------------------------------------------------
%   If i_p = 0, show RMS value
%  ------------------------------------------------------

% 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

  fprintf ('Begin component value carpet plots: \n')
  if ( nargin == 0 )
    i_p = 0 ; y_p = 0. ;
  elseif ( nargin == 1 )
    y_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

  load scp_node_ave_fluxes.tmp
  nr = size (scp_node_ave_fluxes, 1);
  if ( nr == 0 )
    error ('Error missing file scp_node_ave_fluxes.tmp')
  end % if error
  max_p = size (scp_node_ave_fluxes, 2) ; % number of columns
  fprintf ('Read %g nodal stress values \n', nr)
  fprintf ('     with %g components each \n', max_p)
  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 (np)      = 0.       ;       % pre-allocate array z

%                set constants

  % msh_bc_xyz has: pre_p items then: x, y
  y = msh_bc_xyz (1:np, (pre_p+2)) ; % extract x column
  ymax = max (y) ; ymin = min (y) ; diff = ymax - ymin ;
  tol = abs ( diff / (10 * np) ) ;

  given = 0 ;
  for j = 1:np ; % check all nodes
    if ( abs (y(j) - y_p) <= tol ) % found a point
     given = given + 1 ;
     x (given) = msh_bc_xyz (j, (pre_p+1)) ; % extract y

     if ( i_p >= 1 & i_p <=3 )
       z(given) = scp_node_ave_fluxes(j, i_p) ;
     elseif ( i_p == 4 ) % Von Mises Stress
       root_2 = sqrt (2.) ;
       temp = (scp_node_ave_fluxes (j, 1) ...
            -  scp_node_ave_fluxes (j, 2))^2 ...
            +  scp_node_ave_fluxes (j, 1)^2 ...
            +  scp_node_ave_fluxes (j, 2)^2 ...
            +  scp_node_ave_fluxes (j, 3)^2 * 6 ;
       z (given) = sqrt ( temp ) / root_2 ;
     else % i_p = 0, get root mean sq
       z (given) = sqrt(sum(scp_node_ave_fluxes(j,1:max_p).^2));
     end % if get RMS value
   end % if tol
  end % for j

%    Cite max, min values
  if ( given > 0 )
     [V_X, L_X] = max (z(1:given)) ;
     [V_N, L_N] = min (z(1:given)) ;
     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)
     if ( V_X == V_N ) % constant
       V_X = V_X + 2;
     end % if
  end % if given 

%    Initialize plots
   xmax = max (x(1:given))      ; xmin = min (x(1:given)) ;
   zmax = max (z(1:given))      ; zmin = min (z(1:given)) ;
   clf                               % clear graphics
   axis ([xmin, xmax, zmin, zmax])   % set axes
   axis ('square')

   hold on                           % hold image for plots
   xlabel (['X for ', int2str(given),' Nodes at Y = ', ...
            num2str(y_p)])           
   if ( i_p > 0 )
     ylabel (['Flux  (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
     title(['Nodal FEA SCP Flux Component\_',int2str(i_p)])
   else % i_p = 0, get root mean sq
     ylabel (['Nodal RMS Flux Value (max = ', ...
     num2str(V_X), ', min = ', num2str(V_N), ')'])
     title(['Nodal RMS SCP Flux Value'])            
   end % if get RMS value
   plot(x(1:given), z(1:given),'k*')
   grid
   [y(1:given),i_sort] = sort( x(1:given) ) ;
   plot(x(i_sort), z(i_sort), 'k-');

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