Parallel Processing code question, with error Subscripted assignment between dissimilar structures

I am trying to become familiar with the parallel toolbox and wrote what I think is a simple script that is failing and I don't understand why. I have included the code below.

clear all
close all

dataSetSize = 1024;

for x = 1:4:dataSetSize
    Data(x).dataSet = rand(128,256);
    Data(x+1).dataSet = rand(128,512);
    Data(x+2).dataSet = rand(64,128);
    Data(x+3).dataSet = rand(32,64);
end

parpool(4);
parfor x=1:dataSetSize
    Data(x).plotData = 20*log10(abs(fft(Data(x).dataSet)));
end

I get the error

Error using parallelTest (line 15)
Subscripted assignment between dissimilar structures.

Line 15 is the line of the parfor loop. When I execute this as a regular loop it executes fine. I don't see any dependencies and think this should be able to run in parallel.

Any help would be greatly appreciated.

Thanks

Answer 1

[Walter Roberson]

You need to initialize the PlotData field before the loop. Even if you initialize it to [] that would be fine. In your code, the result of the parfor is a structure with a different set of fields than the original, and there are problems copying the data back because of that. Don't create new struct fields inside a parfor.

[Carey Smith]

Great help.