Error when plotting in parfor loop

I'd like to plot inside a parfor loop, but am getting an error I don't understand.

parfor i=1:10
figure;
end
Cannot set WindowStyle to 'docked' when MATLAB is
started with no display or when the -noFigureWindows
option is specified.

I have changed my default window style but got the same error

set(0,'defaultfigurewindowstyle','normal')
set(0,'defaultfigurewindowstyle','docked')

[Mark Sherstan]

Are you running any other code before the loop? What version of MATLAB and parrallel toolbox are your using?

Answer 1

[David Perlmutter]

I get the following

parfor i=1:5
    figure(i)
    plot(rand(i*10,1));
    saveas(gcf,['temp' num2str(i) '.jpg']);
end
Cannot set WindowStyle to 'docked' when MATLAB is started with no display or
when the -noFigureWindows option is specified.

Maybe I have some default settings that are preventing graphics objects from opening in my parallel workers?

[Walter Roberson]

It does sound like you have set(0,'defaultfigurewindowstyle','docked') in effect. Check for a startup.m that might be setting it.

Answer 2

[Walter Roberson]

It is never possible to plot to the display inside any parallel construct. The workers are in separate processes that do not have access to the graphics subsystem.

You would need to either:

1. Calculate all of the data in the parfor and then do the plotting after the parfor; or
2. Use parallel.pool.DataQueue or parallel.pool.PollableDataQueue and send() data back to the client to do the plotting such as by using foreach

Answer 3

[David Perlmutter]

No other code. The error occurs just after opening a new matlab instance.

I'm using Parallel Computing Toolbox Version 6.11 (R2017b)

Answer 4

[Mark Sherstan]

To save a figure in a parfor loop you must do the following as found here. Otherwise save the data and plot after as mentioned by Walter.

parfor i=1:5
    figure(i)
    plot(rand(i*10,1));
    saveas(gcf,['temp' num2str(i) '.jpg']);
end

Try the code above and let us know if the error continues.

Answer 5

[David Perlmutter]

According to this, it should be possible for parallel workers to plot:

https://www.mathworks.com/matlabcentral/answers/68848-is-there-a-way-to-plot-to-a-file-while-in-a-parfor-loop

I don't mind my plots being invisible, but I would like to save them to view later.

Note: I get the same error if I use the "plot" command instead of the "figure"command

[Walter Roberson]

Note that the plots are not just "invisible": they are in a different process. You would need to save them or else find a way to bring back the figures.

Answer 6

[David Perlmutter]

Turns out startup.m was the problem!

I had several default plotting settings, including set(0,'defaultfigurewindowstyle','docked'), in my startup.m

When I comment them all out, I am able to create plots on parallel workers without error.

Thanks Walter and Mark!

[Jackson Jewett]

Could you clarify this? Are you able to display plots within a forloop? Could you advise what you commented out in order to see these results? Thank you!

[Walter Roberson]

David was saving the plots inside the loop; see https://www.mathworks.com/matlabcentral/answers/436570-error-when-plotting-in-parfor-loop#answer_353192

You can save plots inside of parfor; you just cannot display them to the user from inside of the parfor.