How can I plot multiple plots on the same figure using parfor

Hi,

I am running an FEA code and the plotting is what takes most of the time as I am plotting 13000 elements.

Basically, I am trying to leverage the parallel computing and the gpu to optimize the plotting of this example (simplified example):

tic
x = linspace(1,10);

parfor i=1:20
    y(i,:)=x.^((i+1)/i);
end

figure
hold on
for i = 1:20
    plot(x,y(i,:))
end
hold off
cputime=toc

I got the gpu running already by using gpuArray the following way:

tic
x = gpuArray(linspace(1,10));

parfor i=1:20
    y(i,:)=x.^((i+1)/i);
end

figure
hold on
for i = 1:20
    plot(x,y(i,:))
end
hold off

gputime=toc

but how do I use the parfor for the plot function?

if I do this:

tic
xx = linspace(1,10,1000);

parfor i=1:20
    yy(i,:)=xx.^((i+1)/i);
end

figure
hold on

parfor i = 1:20
    plot(xx,yy(i,:))
end

hold off

cpuparalleltime=toc

I get a empty figure

moreover, the fastest running code seems to consistently be the single threaded cpu task.

Thank you everybody

Answer 1

[Walter Roberson]

You cannot do that directly. The workers do not have access to the display, and also do not have concurrent access to the graphics objects already created.

What you can do is:

figs = cell(4,1);
parfor K = 1 : 4
   figs{K} = figure();
   ax = axes('Parent', figs{K});
   h = plot(ax, rand(1,20));
end

This creates independent figures, but after the figures are created the figure structure (and all its children) are copied back to the client. At that point you can merge them all together by extracting the axes children and copyobj() them into the axes you want them all to appear in.

[Gi Ru]

Hi thanks,

I tried it like this:

clc, clear all, close all

x =gpuArray(linspace(1,10));
li=10;
y=gpuArray(zeros(li,length(x)));

parfor i = 1 : li
    y(i,:)=gpuArray(x.^((i+1)/i));
end

%%%% parallel plotting
tic
figs = cell(li,1);

parfor K = 1 : li
   figs{K} = figure('Visible','Off');
   ax = axes('Parent', figs{K});
   h = plot(x, y(K,:));
end

for K = 2 : li
    copyobj(findobj(K,'type','line'),findobj(1,'type','axes'));
end

fp=toc


%serial plotting

tic

figure
for i=1:li
    plot(x,y(i,:))
end

fs=toc

but unfortunately, the parallel version is about 10 times slower than the serial one. In the end, when I have a lot of lines to put on a plot, what method would be the most efficient one? As in my application, it takes me 2 min to run my code to get the results and about 15 min to plot those results.

THanks