function truss_plot(bars, nodes, option, nodes2)
%
% plot a truss.
%
% input:
%
% bars    integer( m, 2) 
%         The i-th row contains information for bar i in the following form:
%         [ label-of-lower-left-node  label-of-upper-right-node ]
%
% nodes   real( n, 2)
%         The i-th row contains information for node i in the following form:
%         [ x-coordinate-of-node  y-coordinate-of-node ]   
%
% option  integer     [optional]
%         option = 0 bars and nodes are not labeled (default)         
%         option = 1 bars and nodes are not labeled (default)
%
% nodes2  real( n, 2) [optional]
%         Second set of node coordinates. The size and format of nodes2 are
%         the same as those of nodes.  If nodes2 contain the coordinates
%         of the deformed truss, both deformed and undeformed truss can
%         be displaayed simultaneously.
%         

if( nargin < 2 )
    error('bars and nodes must be specified') ;
end

if( nargin == 2 )
    option = 0;
end

% check if there is a window 'truss_plot'
fig = findobj('tag','truss_plot');
if length(fig) > 0
   % A window 'truss_plot' exists. Activate it for the plots.
   set(fig,'visible','on');
   figure(fig); clf;
else
   % Create a new window 'truss_plot'.
   fig = figure('Units','normalized',...
                'resize','on','tag','truss_plot',...
                'name',' Truss ',...
                'visible','on');
end

% get number of bars (m) and number of nodes (n)
m = size(bars,1);
n = size(nodes,1);

% plot the bars
for i = 1:m
    x = [nodes(bars(i,1),1), nodes(bars(i,2),1)];
    y = [nodes(bars(i,1),2), nodes(bars(i,2),2)];
    plot(x,y,'b'); hold on
end
% plot the nodes
plot(nodes(:,1),nodes(:,2),'bo'); hold on

% enlarge x and y axis
xmin  = min(nodes(:,1));
xmax  = max(nodes(:,1));
ymin  = min(nodes(:,2));
ymax  = max(nodes(:,2));
xscal = max([abs(xmin),abs(xmax)]);
yscal = max([abs(ymin),abs(ymax)]);
xmin  = xmin-0.1*xscal;
xmax  = xmax+0.1*xscal;
ymin  = ymin-0.1*yscal;
ymax  = ymax+0.1*yscal;
axis([ xmin xmax ymin ymax ]); axis equal;

% label bars and nodes 
if( option > 0 )
%   Label the bars
    for i = 1:m
        x = [nodes(bars(i,1),1), nodes(bars(i,2),1)];
        y = [nodes(bars(i,1),2), nodes(bars(i,2),2)];
        h = text(0.45*x(1)+0.55*x(2),0.45*y(1)+0.55*y(2),int2str(i));
        set(h,'Color','k','FontSize', 14, 'FontWeight', 'bold');
    end
%   Label the nodes
    for i = 1:n
        h = text(nodes(i,1),nodes(i,2),int2str(i));
        set(h,'Color','k','FontSize', 14, 'FontWeight', 'bold' );
    end
end

if( nargin > 3 )
    % plot the bars
    for i = 1:m
        x = [nodes2(bars(i,1),1), nodes2(bars(i,2),1)];
        y = [nodes2(bars(i,1),2), nodes2(bars(i,2),2)];
        plot(x,y,'r--'); hold on
    end
    % plot the nodes
    plot(nodes2(:,1),nodes2(:,2),'ro'); hold on

    % enlarge x and y axis
    xmin2  = min(nodes2(:,1));
    xmax2  = max(nodes2(:,1));
    ymin2  = min(nodes2(:,2));
    ymax2  = max(nodes2(:,2));
    xscal2 = max([abs(xmin2),abs(xmax2)]);
    yscal2 = max([abs(ymin2),abs(ymax2)]);
    xmin2  = xmin-0.1*xscal;
    xmax2  = xmax+0.1*xscal;
    ymin2  = ymin-0.1*yscal;
    ymax2  = ymax+0.1*yscal;
    xmin   = min([xmin,xmin2]);
    xmax   = max([xmax,xmax2]);
    ymin   = min([ymin,ymin2]);
    ymax   = max([ymax,ymax2]);
    axis([ xmin xmax ymin ymax ]); axis equal;
end