Missing function outputs in some iterations inside parfor

I have a function which is invoked in a parfor loop. The function in turn calls a couple more functions and outputs structure fields. However, I do not get all my results, although my simulation runs correctly.

      parfor i = 1:900
               for j = 1:3600
                [x(i,j),y(i,j).y,y(i,j).z] = func(a,b,c,d);
               end
          end

Here, x,y,z,a,b,c,d are a mix of structures and matrices. So lets assume x is an array. I get correct results in x which tells me that my function runs fine. But a few entries in y (which is a structure) are missing. The missing entries are different at different execution of the same program. Eg: all the columns from row 29 to 41 in y have no entries, but x has the corresponding entries.

What could be the cause? This is my first experience with parallel programming. So any help is appreciated!

Answer 1

[Walter Roberson]

You should be avoiding writing to the same output variable with multiple varying subscripts: it is not permitted at all in older versions and is not as efficient when it is done.

Vectorizing properly is a bit tricky because of your structures.

parfor i = 1:900
   xi = zeros(1,3600); yiy = cell(1,3600); yiz = cell(1,3600);
   for j = 1:3600
    [xi(1,j), yiy{1,j}, yiz{1,j}] = func(a,b,c,d);
   end
   x(i,:) = xi; y(i,:) = struct('y', yiy, 'z', yiz);
end

Note that the above code is only valid for the case where y does not have any existing content that needs to be left intact (such as if there were additional fields of y that you were not writing to but need preserved.)

[Amulya NV]

Thats great!! Thanks a lot.. It is working :)