# Parfor error with bsxfun

2 views (last 30 days)
Cem on 9 Jul 2014
Edited: Matt J on 9 Jul 2014
Dear all,
I'm having a weird issue with using parfor and bsxfun. I provide a minimal working example below (tried on both 2011b and 2013a). The version with for is working fine, whereas if I switch to parfor, I receive the 'non-singleton dimensions must match' error for bsxfun. I'm not sure if this was already answered although I looked for possible related questions&answers. Thanks in advance.
Cem
var1=repmat((1:1000)',2,3);
var2=ones(1000,1000);
var3=ones(6000,1);
temporary_var=bsxfun(@times,var2(var1,:),var3);
result=zeros(1000,1000);
for i=1:1000
result(i,:)=sum(bsxfun(@times,var2(var1,i),temporary_var));
end
Note: the issue persists both matlabpools open and closed.

Jill Reese on 9 Jul 2014
I think that the parfor analysis is getting a bit confused by the multidimensional indexing into var2. If you re-write the code as follows it should work:
var1=repmat((1:1000)',2,3);
var2=ones(1000,1000);
var3=ones(6000,1);
temporary_var=bsxfun(@times,var2(var1,:),var3);
result=zeros(1000,1000);
tmp = var2(var1,:);
parfor i=1:1000
result(i,:)=sum(bsxfun(@times,tmp(:,i),temporary_var));
end
Matt J on 9 Jul 2014
@Cem,
If this is what you want, the parfor loop looks like a doubtful way to go about it. A loop-free computation of the same result is
result=tmp.'*temporary_var;
which would likely have better internal optimization/parallelization than parfor.

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