Matlab – Real time plot in MATLAB

animationgraphicsMATLABplotreal time

I'm very new to MATLAB and I was trying to display a real time plot of some calculations. I have an N sized vector and I work with m values at a time (say m = N/4), so I want to plot the first m values and then as soon as the second m values are calculated have them replace the first plot.

My approach was as follows:

for i=1:N,
  ...
  //compute m
  ...
  plot(m);
end;

but it fails to update the plot in every loop and waits for all the loops to finish to plot the data. My question is: Should I use another function instead of plot or could I add some delay in each loop?

I think there must be a way I'm not aware of for updating the plot instead of re-plotting it every time.

Best Answer

As Edric mentioned, you'll definitely want to include a drawnow command after the call to plot to force an update of the graphics. However, there is a much more efficient and smoother method to animate plots that doesn't involve recreating the entire plot each time. You can simply initialize your plot, capture a handle to the plot object, then modify the properties of that object in your loop using the set command. Here's an example:

hLine = plot(nan);         % Initialize a plot line (which isn't displayed yet
                           %   because the values are NaN)
for i = 1:N                % Loop N times
  ...
  % Compute m here
  ...
  set(hLine, 'YData', m);  % Update the y data of the line
  drawnow                  % Force the graphics to update immediately
end

In addition, before your loop and after the call to plot you can set a number of axes properties, like the axes limits, etc., if you want the axes to stay fixed and not change their appearance with each new vector m that is plotted.

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R – Plot two graphs in same plot in R

lines() or points() will add to the existing graph, but will not create a new window. So you'd need to do

plot(x,y1,type="l",col="red")
lines(x,y2,col="green")

Matlab real time plot

Instead of doing a high-level plot call, consider adjusting the line handle properties, more specifically the XData and YData, in the loop:

figure(1);
lHandle = line(nan, nan); %# Generate a blank line and return the line handle

for i = 1:1000
    X = get(lHandle, 'XData');
    Y = get(lHandle, 'YData');

    X = [X i];
    Y = [Y i];

    set(lHandle, 'XData', X, 'YData', Y);
end

Doing it this way, a tic/toc before/after the code gives 0.09 seconds; a naive plot as you have, as you have probably seen, gives a runtime of nearly 20 seconds.

Note that I only used get in this example to generate the dataset; I assume for a real time plot you've got some DatasetX and DatasetY to plot, so you'll need to work your data accordingly. But in the end, once you've got the dataset you want to plot at a particular time, just set the line's entire XData and YData.

Finally, note that this set call gets a bit unwieldy for very large datasets, since we have to set the the lines' data every time rather than append to it. (But it's certainly still faster than using plot.) This might be good enough depending on how frequently your dataset changes. See this question for more details.

EDIT: As of MATLAB R2014b, the animinatedline object makes it easier to plot points from streaming data:

Animated line objects optimize line animations by accumulating data from a streaming data source. After you create the initial animated line using the animatedline function, you can add new points to the line without having to redefine the existing points. Modify the appearance of the animated line by setting its properties.

Best Answer

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Matlab real time plot

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