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Parfor Step

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Brian
Brian on 11 Jun 2012
I am attempting to run a ParFor statement with a step function and Matlab is giving me an error "The range of a parfor statement must be increasing consecutive integers. See Parallel Computing Toolbox, "parfor"." I'm wondering if this is possible or if I have to do some manipulation to my loop to get this to work in parallel. Would someone be able to make a suggestion as to how to modify one of these loops so that it will work in parallel?
Simplified Example
parfor (i = 1:10:75,8)
test3(i)= i*3;
end
Real Example
parfor (i = 1:10:75,8)
tic
recnum = min(i+9,length(test));
datainsert(conn,'dbo.tbl_FactorExposure_Security',{'CUSIP','MktDate','Factor_Exp','Factor_Num'},MyData(i:recnum,:));
disp(i)
toc
end
Thanks a lot! Brian
  2 Comments
Brian
Brian on 11 Jun 2012
Yeah, sorry for being unclear. In my real example I am breaking up the size of my datainsert command by using a step function. I'm doing this because I'm inserting about 28 million records and the java heap size in Matlab is running out of memory. SInce I'm breaking it up, I'd like to do the datainsert in parallel so that it's not so slow.

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Accepted Answer

Edric Ellis
Edric Ellis on 12 Jun 2012
As the doc states, PARFOR needs to work with unit-step ranges. So you do need to re-work the loop slightly, something like this:
idx = 1:10:75;
parfor (i = 1:numel(idx), 8)
val = idx(i);
test3t(i) = val * 3;
end
That example leaves 'test3t' slightly different to 'test3' in your example, you can rearrange things by doing
test3(idx) = test3t;
  2 Comments
Edric Ellis
Edric Ellis on 12 Jun 2012
By the way, the syntax using the extra parentheses around the PARFOR arguments is rarely needed, it's much simpler just to write "parfor i = 1:numel(idx)".

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