CODEWITHSUNDEEP
matlabparallel-processingexecution
ammar
ammar

Reputation: 33

Parallel execution in MATLAB

In MATLAB, when I use the numlabs instruction in the Command Window after calling parpool(4), it is 1. But, when I use the same instruction in the parallel command window it is 4, Why?

>> parpool(4)
Starting parallel pool (parpool) using the 'local' profile ... connected to 4 workers.

ans = 

 Pool with properties: 

            Connected: true
           NumWorkers: 4
              Cluster: local
        AttachedFiles: {}
          IdleTimeout: 30 minute(s) (30 minutes remaining)
          SpmdEnabled: true

>> numlabs

ans =

     1

>> pmode start
Starting pmode using the 'local' profile ... connected to 4 workers.

numlabs 4 4 4 4

Upvotes: 1

Views: 376

Answers (2)

horchler
horchler

Reputation: 18494

numlabs returns the "total number of workers operating in parallel on current job". If you type the command after starting a pool, there obviously won't be any ongoing job. Also from the numlabs documentation:

In an spmd block, numlabs on each worker returns the parallel pool size.

However, inside a parfor-loop, numlabs always returns a value of 1.

If you just want the number of workers, you can use gcp (get current pool):

hp = gcp;
hp.NumWorkers

Upvotes: 3

Benoit_11
Benoit_11

Reputation: 13945

I think that is normal behavior, since numlabs should return 1 when not used inside a spmd block or during a parallel job. What you have done above is only open the parallel pool, but not asking it to do a parallel job.

I can't test right now, but if you call something like this:

spmd

   some statement with numlabs

end

you will see printed in the Command Window that you are indeed using the 4 available workers.

Upvotes: 2

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