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Error when plotting in parfor loop

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David Perlmutter
David Perlmutter 2018-12-19
评论： Walter Roberson 2021-9-3
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')
  1 个评论
Mark Sherstan
Mark Sherstan 2018-12-19
Are you running any other code before the loop? What version of MATLAB and parrallel toolbox are your using?

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采纳的回答

David Perlmutter
David Perlmutter 2018-12-19
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?
  1 个评论
Walter Roberson
Walter Roberson 2018-12-19
It does sound like you have set(0,'defaultfigurewindowstyle','docked') in effect. Check for a startup.m that might be setting it.

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更多回答（5 个）

Walter Roberson
Walter Roberson 2018-12-19
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
David Perlmutter
David Perlmutter 2018-12-19
No other code. The error occurs just after opening a new matlab instance.
I'm using Parallel Computing Toolbox Version 6.11 (R2017b)
Mark Sherstan
Mark Sherstan 2018-12-19
编辑：Mark Sherstan 2018-12-19
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.
David Perlmutter
David Perlmutter 2018-12-19
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
  1 个评论
Walter Roberson
Walter Roberson 2018-12-19
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.

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David Perlmutter
David Perlmutter 2018-12-20
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!
  2 个评论
Jackson Jewett
Jackson Jewett 2021-9-3
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
Walter Roberson 2021-9-3
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.

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