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Re: Parallel computing with Mathematica 7?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95368] Re: Parallel computing with Mathematica 7?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 17 Jan 2009 05:26:09 -0500 (EST)
  • References: <gkppvv$dsp$1@smc.vnet.net>

Hi,

 > Does anybody have a positive experience with parallelization in
 > Mathematica 7?

yes, but your example

> Timing[ParallelTable[Element,{i,1,2}]]
> 
> where Element = Tr[MatrixExp[A]] and A is a large latrix.

is a very stupid one. You can't expect that the distribution
of a large matrix A to the kernels will not need the
most of the time, while the computation of the expression
itself is so quick that you will never see a speed up.
Since the master kernel does the most work when
it distribute the matrix to the other kernels (
and this is a serial task), you see only
this in the processor load.

Successful parallelization, i.e., one with a speed up,
is a hard work and not a matter
of putting Parallel*[] in every possible position.

BTW: A parallel program should be slower than a serial one.
Only in a few cases this is not the case.

Regards
   Jens

einschlag at gmail.com wrote:
> I have installed Mathematica 7 on my new laptop (Intel Centrino double
> core, Windows XP) and the first thing I tried was the long awaited
> parallllllel computing. I have tried different new commands and what I
> saw was a black box with input and no output. I could not see any
> evidence that parallelization works for me.
> 
> My basic test was to create a table of two equal elements being the
> trace of the exponential of a large matrix. One such operation takes 8
> sec., so the sequential computation of the table requires the double
> time being 16 sec. Parallelization should reduce the time to 8 sec.
> However, this does not happen. Here is the code that I used:
> 
> Timing[ParallelTable[Element,{i,1,2}]]
> 
> where Element = Tr[MatrixExp[A]] and A is a large latrix.
> 
> I have looked at the system performace in the Windows Task Manager.
> Both with Table and ParallelTable the processor load was 50%, that is,
> only one core of the two was working.
> 
> In addition, I have found that the command Parallelize does not take
> the option Method->"..."
> 
> Does anybody have a positive experience with parallelization in
> Mathematica 7? Do I have to perform a special setup to get these
> features working? I tried different ...Kernel... manipulations to no
> avail.
> 
> Dmitry
> 


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