Question about parforloop in matlab
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Hi, I am using parfor loop on matlab. However, I am having troubles with printing to a file using fprintf command. I am getting the following error:
Invalid file identifier. Use fopen to generate a valid file identifier.
Please Help!
Here's my code:
tic
i = 1;
fID = fopen('datafile7.txt', 'W');
fprintf(fID,'name\trow\tcolumn\t25R\t25G\t25B\t1R\t1G\t1B);
s = ['photo000' int2str(i) '.jpg'];
A=imread(s);
[m,n,rgb]=size(A);
for row=4:(m-3)
parfor column=4:(n-3)
fprintf(fID, 'image%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\t\r\n',i,row,column,A(row-3:row+3,column-3:column+3,1), A(row-3:row+3,column-3:column+3,2), A(row-3:row+3,column-3:column+3,3) );
end
end
fclose(fID);
toc
5 Comments
Adam
on 29 Oct 2014
If you use a matfile (doc matfile) you can write to the same file using a parfor loop, but it is not necessarily very performant.
I do it for a computationally expensive algorithm, but I never had time to work out how of it it is possible to have a thread doing the file writes while the rest of the threads get on with their next bit of processing so my algorithm has ~10% downtime writing block results to a matfile. It does work though .
Answers (2)
Sean de Wolski
on 29 Oct 2014
Rather than writing results to the same file, write to N files and concatenate them later where N is the number of workers you have.
4 Comments
Matt J
on 29 Oct 2014
Edited: Matt J
on 30 Oct 2014
I have to create a distance matrix for the image an then conduct a KNN search for skin segmentation.
I don't have a clear picture of what that means, but if the processing operates on one 7x7 image block at a time, why not use
blockproc(..., 'UseParallel',1)
to obtain the final result directly?
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