Parfor Step

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Brian
Brian 2012-6-11
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 个评论
Walter Roberson
Walter Roberson 2012-6-11
Sorry? What do you intend
for (i = 1:10:75,8)
to mean? Is it intended as
for i = [1:10:75, 8]
meaning
for i = [1 11 21 31 41 51 61 71 8]
?
Brian
Brian 2012-6-11
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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Edric Ellis
Edric Ellis 2012-6-12
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 个评论
Brian
Brian 2012-6-12
Thanks a lot Edric. I am still new to Matlab and frankly, sometimes the documentation, although very thorough, goes right over my head.
Brian
Edric Ellis
Edric Ellis 2012-6-12
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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