MATLAB: How can I move a Point in a plot (GUI) from one side to the other in a fixed time

accuracyguimoveplottime

I have a point in a plot and I want to move it "smoothly" to the other side of the plot within a fixed amount of time. In the example this time is 3s, and I refresh the plot "every 20ms" (20ms is what I want, but it's always more, between: 30 and 50ms). My code is:
interval=3000/20; %3000/20=150
a=0;
for i=1:1:interval
      iTime=clock; 
      set(pointHandle,'Xdata',point(1).coordinatesNow(1)+(500/150),'Ydata',point(1).coordinatesNow(2)); %Only refresh Xaxis
      point(1).coordinatesNow(1)=point(1).coordinatesNow(1)+(500/150);
      pause(0.02); %pause of 20ms
      a=a+etime(clock,iTime); %total elapsed time
end
    disp(a); %show total time
So I'd like "a" to be 3s, but most of the times is between 7 and 10s, How could I get more accuracy?

Best Answer

edit: changed timing to an overall target for loop instead of interval time.
See the code below:
 figure;
 ax = axes;
 x = [0:100];
 h = plot ( ax, x, x*0 );
 ax.YLim = [0 100];
 targetTime = 3;
 nSteps = 100;
 intervalTime = targetTime./nSteps;
 loop = tic;
 for ii=1:nSteps
   h.YData(:) = ii;
   drawnow();
   timeTaken = toc(loop);
   % comment out this line to see the effet of the pause
   pause(max(0,(intervalTime.*ii)-timeTaken));
 end
 toc(loop)
When I run this in matlab I get the following:
 Elapsed time is 1.174296 seconds.   (pause commented out)
 Elapsed time is 3.006906 seconds.
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