For loop is taking a lot of time to execute.

I have to change four diagrams during the execution of one for loop. I'm using subplot to plot all the diagrams in one. But the loop takes too long for execution. I think it is because of the function "figure" being called every time. But if I'm not including figure after every loop execution it isn't showing the plot. All the variables in the code are matrices(eg. barax(i,;)). pos is the handle for the figure.

        pos = figure('units','normalized','position',[0 0 1 1],'color','b',...
            'menubar','none','numbertitle','off','name','WW_QuickReturn');

        for i = 1:div
                          if strcmp(get(pb,'string'),'Start')
                              return
                          end
                          figure(pos)
                          %%Stimulation
                          subplot(2,2,1)
                          set(subplot(2,2,1),'XTickLabel',[],'YTickLabel',[],'XLim',[xmin xmax],'YLim',[ymin ymax],'XTick',0,'YTick',0)
                          hold on
                          title ('Stimulation','fontweight','bold','fontsize',20,'color','w')
                          cla;
                          plot(barax(i,:),baray(i,:),'b',barbx(i,:),barby(i,:),'g',barcx(i,:),barcy(i,:),'c','linewidth',5);
                          plot(0,0,'ok')
                          plot(0,0,'sk','MarkerSize',12)
                          plot(0,-1*d,'ok')
                          plot(0,-1*d,'sk','MarkerSize',12)
                          plot([min(x4)-20,max(x4)+20],[y4-10.5,y4-10.5],'k','linewidth',7)
                          fill(xset1(i,:),yset1(i,:),'r');
                          fill(xset(i,:),yset(i,:),'r');
                          hold off
                          %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
                          %%Velocity Diagram
                          subplot(2,2,2)
                          title ('Velocity Vector','fontweight','bold','fontsize',20,'color','w')
                          hold on
                          cla;
                          set(subplot(2,2,2),'XTickLabel',[],'YTickLabel',[],'XLim',[min(Vc) max(Vc)],'YLim',[1.5*min(Va*sin(t)) 1.5*max(Va*sin(t))],'XTick',0,'YTick',0)
                          quiver(0,0,Va*sin(-t(i)),Va*cos(-t(i)),0)
                          h1 = text(Va*sin(-t(i))/2,Va*cos(-t(i))/2,'Va');
                          set(h1,'Rotation',-t(i)*180/pi);
                          quiver(Va*sin(-t(i)),Va*cos(-t(i)),-Vc(i)-Va*sin(-t(i)),-Va*cos(-t(i)),0)
                          h2 = text((-Vc(i)+Va*sin(-t(i)))/2,(Va*cos(-t(i))/2),'Vca');
                          set(h2,'Rotation',atan(-Va*cos(-t(i))/2/(Vc(i)-Va*sin(-t(i))/2)));
                          quiver(0,0,-Vc(i),0,0)
                          text(-Vc(i)/2,0,'Vc');
                          hold off
        end

Can anyone suggest how to reduce the execution time.

[Geoff Hayes]

Dhruv - how many iterations are you looping over? What is div? Perhaps rather than creating a new figure, just use one and update the existing plots rather than creating new ones (i.e. update the XData and YData of the plot). Also, at the end of each iteration (of your for loop) add a drawnow or pause(0.001) so that the updated plots can be drawn on the figure (maybe this is why you are creating a new figure each time).

[Stephen23]

Geoff Hayes is right: using one figure and updating XData and YData is invariably faster.

[Dhruv Thakkar]

Geoff Hayes div is the number of divisions used for calculating the variables for example

div = 100
  t = linspace(0,2*pi,div);
    %%Vc is defined in the calculation as follows
Vc  = Va.*sin(t);

Thanks Geoff using drawnow reduced the execution time a bit. Is there any other thing I should do to still increase the speed. The current execution time for one loop is 0.09 seconds(found using tic;toc;)

[Geoff Hayes]

Dhruv - what did you do to reduce the number of execution times? Add the drawnow or pause, or did you add code to update the plot on each iteration (rather than create a new one)?

[Dhruv Thakkar]

Geoff Hayes - I used drawnow removing the "figure(pos)" line but there wasn't much of a difference. With "figure(pos)" it took 0.13sec/iteration, now it takes 0.09sec/iteration.

If I can further reduce the time it would be very useful for me. Thank you.

PS. pause and drawnow gave nearly the same result.

[Geoff Hayes]

ok, so try updating the plot on each iteration of the loop. here is a quick example

x = -2*pi:0.01:2*pi;
y = sin(x);
figure;
hPlot = plot(NaN,NaN);
xlim([x(1) x(end)]);
ylim([min(y) max(y)]);
for k=1:length(x)
   xdata = [get(hPlot,'XData') x(k)];
   ydata = [get(hPlot,'YData') y(k)];
   set(hPlot,'XData',xdata,'YData',ydata);
   pause(0.01);
end

Note how we call plot once and then update the x and y data for that plot on each iteration of the loop.