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Re: Re: Re: Multicore Calculations

  • To: mathgroup at
  • Subject: [mg60880] Re: [mg60862] Re: [mg60809] Re: [mg60769] Multicore Calculations
  • From: Jeff Bryant <jeffb at>
  • Date: Sat, 1 Oct 2005 02:55:57 -0400 (EDT)
  • References: <> <> <>
  • Sender: owner-wri-mathgroup at

   Mathematica on Linux-x86-64 supports multithreading on multicore and 
  multiprocessor systems. You can set the number of threads with the 
OMP_NUM_THREADS variable, eg a value of 1 will disable threading and a 
value of 4 will use three threads. By default Mathematica uses all 
processors (physical or virtual) listed in /proc/cpuinfo. None of  this 
changes the fact that BLAS level 1 and 2 operations don't  parallelize well.


Manuel Schmidt wrote:
> Hi, 
> this are the informations about my system:
> Dual Opteron
> 2G RAM
> SuSE Prof. 9.3
> Mathematica 5.2
> The threads do not show up independently on this system (it is a
> cip-pool). On my local computer, I have only one processor (Athlon64)
> with Gentoo (I know, it is not supported) running and there the kernel
> uses 4 processes. Can one set from outside (as user or installer) how
> many Threads a kernel uses?
> Thanks,
> Manuel
> On Thu, 2005-09-29 at 05:41 -0400, Jeff Bryant wrote:
>>   The results you get depend on a couple of factors.  I'll provide a 
>>couple comments and perhaps other, more qualified people can respond 
>>directly if necessary for additional details.
>>What platform (CPU and OS) are you running on? That will determine if
>>a) we support multiple processors/cores
>>b) if top shows threads independently  of their parent process.
>>Also, vector-vector (BLAS level 1) and matrix-vector operations (BLAS 
>>level 2) don't parallelize terribly well, so there will be little 
>>benefit to multiple processors for those types of operations, anyway.
>>Manuel Schmidt wrote:
>>>Hi all,
>>>i'm wondering, how one can convince the MathKernel to do a numerical
>>>linear algebra calculation on two processors at the same time in 5.2.
>>>Am I right, that this should be computed on two processors (if
>>>vec1 = Table[Random[], {i, 5000000}];
>>>vec2 = Table[Random[], {i, 5000000}];
>>>While[True,Dot[vec1, vec2]]
>>>or a big matrix and a vector
>>>Anyways, I see in top only one kernel running. There is only one thread.
>>>Are there different binaries for the multicore and the singlecore

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