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ParallelTable[ ]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100768] ParallelTable[ ]
  • From: "Scot Martin" <smartin at seas.harvard.edu>
  • Date: Sat, 13 Jun 2009 06:04:21 -0400 (EDT)
  • Organization: Harvard University
  • Reply-to: <scot_martin at harvard.edu>

Just started looking at the parallel computing. This seems a very good
option for me because any "long" calculations I have are usually tied to
list manipulation.

 

For background,$ProcessorCount returns "2" on my machine. 

 

I tried this command:

 

AbsoluteTiming[ParallelTable[i^2, {i, 1000000}]]

 

The required time was 9.28 s.

 

 

I followed with this command:

 

AbsoluteTiming[Table[i^2, {i, 1000000}]]

 

The requied time was 0.86 s.

 

 

 

So, you can imagine my confusion. Can anyone explain why parallel table
generation took 10 times as long?

 

 

[Incidentally and perhaps related, the command of Timing[ParallelTable[i^2,
{i, 1000000}]] takes 0.078 s. This leaves me very confused because the
computer obviously take much longer to execute, i.e., I am sitting at my
console for closer to 9.28 s than 0.078 s. The command of Timing[Table[i^2,
{i, 1000000}]] takes 0.875 s. What gives?]

 

 

Looking forward to everyone's insights!


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