function  eigen_modes_graph (i_p, first) 
% Copyright 2004, J.E. Akin.  All rights reserved.
%  ------------------------------------------------------
%  Matlab graph of i_p-th component value of 1 eigenvector, 
%  at mesh node 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

  clear fid_1 fid_5 
  if ( nargin == 0 )
    i_p = 1 ; first = 1 ; 
  elseif ( nargin == 1 )
    first = 1 ; 
  end % if

  step_1 = first         ; 
  fprintf ('Mode selected =  %g \n', step_1)
  save_1 = step_1; 
  if ( step_1 > 999 )
    save_1 = mod(step_1,999)
  end % if

%    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 > 1 )
    %b error ('This is not a 1D mesh')
    fprintf ('Not 1D: will use x-coordinate only \n')
  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)

  ng = 1 ; % number of generalized dof
% ==================== 4 files ====================
  if ( save_1 < 10 )
    file_1 = ['node_results_00',  int2str(save_1)];
  elseif ( save_1 < 100 )
    file_1 = ['node_results_0',  int2str(save_1)];
  else
    file_1 = ['node_results_',  int2str(save_1)];
  end % if
  filename_1 = [file_1, '.tmp'];
  fid_1= fopen(filename_1, 'r') ;

%    load the file array
  Result_1 = fscanf (fid_1, '%g  \n', [inf]) ;
  NP = size (Result_1, 1) ;
  if ( NP == 0 )
    error ('Error missing file ', file_1, '.tmp')
  end % if error
  if ( NP ~= np )
    fprintf ('Read %g nodal dof  \n', NP)
    ng = NP / np ;
    fprintf ('with %g per node \n', ng )
  end % if
  max_p = ng ; 
  if ( i_p > max_p ) 
    error ('i_p > available data')
  end % if error
  Result_1 = reshape (Result_1, ng, np) ;
  Result_1 = Result_1' ;

      file_5 = ['node_results_000'];
      filename_5 = [file_5, '.tmp'];
      fid_5= fopen(filename_5, 'r') ;
  
  %    load the file array
      Result_5 = fscanf (fid_5, '%g  \n', [inf]) ;
      NP = size (Result_5, 1) ;
      if ( NP == 0 )
        error ('Error missing file ', file_5, '.tmp')
      end % if error
      if ( NP ~= np )
        fprintf ('Read %g system eigen values \n', NP)
      end % if
      mode_1 = Result_5 (step_1) ;


% ==================== end 4 files ====================
  x (np)      = 0.       ;       % pre-allocate array x
  
  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

  if ( i_p >= 1 )
    y_1 = Result_1(:, i_p) ;
  else % i_p = 0, get root mean sq
    for k = 1:np
      y_1 (k) = sqrt ( sum (Result_1 (k, 1:max_p).^2)) ;
    end % for k
  end % if get RMS value

%    Initialize plots
   xmax = max (x)      ; xmin = min (x) ;
   y_1X = max (y_1)    ; y_1N = min (y_1) ;

   ymax = max (y_1X) ;                       
   ymin = min (y_1N) ;                       
       ymax = ymax + abs (ymax)/10. ;
       ymin = ymin - abs (ymin)/10. ;
   if ( ymin == ymax )
     disp(ymin)
     error('All values are the above constant')
   end % if
%b ymax=1.0
   clf                               % clear graphics
   axis ([xmin, xmax, ymin, ymax])   % set axes

   hold on                           % hold image for plots
   xlabel ('X')                      % add label 
   ylabel (['Component ', int2str(i_p), ' (max = ', ...
             num2str(ymax), ', min = ', num2str(ymin), ')'])
   title(['Mode ', int2str(step_1),  ...
          ' Component\_', ...
          int2str(i_p),': ', int2str(nt),' Elements, ', ...
          int2str(np), ' Nodes, (', int2str(nod_per_el), ...
          ' per Element)'])

% plot node values        
   format short
   plot (x, y_1, 'ko')
   legend (['Freq ', int2str(step_1), ' = ', num2str(mode_1)])    
   plot (x, y_1, 'k-')
   grid
 
%       -depsc -tiff            % for an eps version
% print ('-dpsc', ['result_', int2str(i_p), '_eigen_graph_1248'])
  hold off
%  v_text = ['Created result_', int2str(i_p), '_eigen_graph_1248.ps'] ;
% fprintf (1,'%s', v_text) ; fprintf (1, ' \n' )
% end of eigen_modes_graph