How can I plot data as program runs?

I would like to write a program to simulate planets in orbit for many iterations, for example to see if asteroids will form into a stable orbit after many thousands of iterations.

So far all I can find in Matlab is how to plot an equation etc. Matlab only makes the plot after it has finished doing the calculations.

Is it possible to show data as the program runs, showing for example orbits repeatedly over a long time while it continues running?

Do you have any examples of programs that work like that? I am not very familiar with object oriented programming so an example to play with would be very helpful.

Jonathan Pulman

Answer 1

[per isakson]

See Set Handle Graphics object properties

You need to do something like

    set( line_handle, 'Xdata', new_x_ value, 'Ydata', new_y_value )

and see example at the bottom of page Animation

[Jonathan Pulman]

Thank you, I will try that. I don't really undedrstand handles yet so this will help me

[Eugene]

I would use the method by setting the data in the handle. The previous line would be something like:

 figure(1);
 line_handle = plot(x,y);
 while ~finished
     [x,y] = calculate();
     set( line_handle, 'Xdata', x, 'Ydata', y);
 end

As an example:

 >> figure(1); clf
 >> h = plot([1:10],sin([1:10]*2*pi*0.05));
 >> for w=0.01:0.01:0.1; set(h,'Ydata',sin([1:10]*2*pi*w)); pause(1); end

Answer 2

[Image Analyst]

Of course have the plotting call inside your loop, but if it's a really intensive loop you're probably going to have to put in a "drawnow" right after the call to plot() (or whatever function you're using) to get it to refresh/update the screen immediately. And you may or may not want to plot just the last N points, say the last 500 points, so the call to plot doesn't get slower and slower while just painting over the same pixels on the screen.

[Jonathan Pulman]

Thank you. I tried drawnow and it does what I wanted. So are you saying that if I had say 500 points (dots on the screen) on a plot using drawnow, when it adds another single point it would redraw all the previous 500? Although it would not be visible that would slow things down.

[Image Analyst]

It depends on what you want to do. Do you want to ADD one additional point to the existing points? Or do you want to clear all the points and plot just the last 500 or so? How many points describing your orbit do you think you'll eventually have if you let this thing run on and on? Millions?

[Jonathan Pulman]

Sorry for delay; I did not know I got another reply.. Well, millions of calculations if it runs for a long time, but it would be only be useful to show the last, say 500. One orbit might be 500 sets of calculations.

Adding one point to existing ones would look nice (like real time) but I presume storing the last 500 then showing them would be quicker.