Problem with parfor loop (not enough input arguments)

I'm having problem with the following snippet of code:

parfor i = 1:196072
	z = x(i,:);
	z1 = filter(Hd, z);
	fprintf(fid, '%20.6f', z1);
	fprintf(fid, '\n');
end
fclose(fid);  

As soon as I run the code snippet, it says: Not Enough Input Arguments.

However, the code works fine using normal for loop. I tried shutting down and restarting Parpool but no effect. I also tried restarting MATLAB, no effect. I tried deleting local_cluster_jobs folder in C:/Users/AppData/Roaming/MATLAB but no effect.

[Rik]

Can you confirm this also fails with another loop variable? I am personally not a fan of i and j as loop variables because they can be confusing and cause weird bugs.

Another issue might be the fprintf, although that might work as intended. (note that the order of execution is not guaranteed, so the files will be different when created with for or parfor)

[Walter Roberson]

Is Hd possibly a global variable?

[Swapnil Sayan Saha]

I solved it.

The filter function can work in two ways:

• https://www.mathworks.com/help/dsp/ref/filter.html
• https://www.mathworks.com/help/matlab/ref/filter.html

First method: filter function works with a filter object: filter(Hd, x), where Hd is a filter object exported from FilterDesigner... second method: filter function works with filter coefficients: filter(b,a,x), where b and a are filter transfer function coefficients.. x is the signal..

For some reason, parfor loop cannot process Hd.. So i just exported the coefficents in the workspace and used them inside the loop, also made a couple of changes to better optimize memory usage.

fid = fopen('bagaccx_f.txt','w');
fclose(fid);
parfor i = 1:196072
   fid = fopen('bagaccx_f.txt','a');
   fprintf(fid, '%f\t', filter(b,a, x(i,:)));
   fprintf(fid, '\n');
   fclose(fid);
end

Answer 1

[Swapnil Sayan Saha]

I solved it.

The filter function can work in two ways:

• https://www.mathworks.com/help/dsp/ref/filter.html
• https://www.mathworks.com/help/matlab/ref/filter.html

First method: filter function works with a filter object: filter(Hd, x), where Hd is a filter object exported from FilterDesigner... second method: filter function works with filter coefficients: filter(b,a,x), where b and a are filter transfer function coefficients.. x is the signal..

For some reason, parfor loop cannot process Hd.. So i just exported the coefficents in the workspace and used them inside the loop, also made a couple of changes to better optimize memory usage.

fid = fopen('bagaccx_f.txt','w');
fclose(fid);
parfor i = 1:196072
   fid = fopen('bagaccx_f.txt','a');
   fprintf(fid, '%f\t', filter(b,a, x(i,:)));
   fprintf(fid, '\n');
   fclose(fid);
end

[Walter Roberson]

Was Hd a global variable? If so then parfor would have seen it as [] in the workers, as the content of global variables is not copied to workers.

[Swapnil Sayan Saha]

Yes. Maybe that was a problem.