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results from Array and ParallelArray differ

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  • Subject: [mg117011] results from Array and ParallelArray differ
  • From: Peter Pein <petsie at>
  • Date: Mon, 7 Mar 2011 05:49:46 -0500 (EST)

Dear group,

I did a search using tags "ParallelArray" and "Join" and did not find 
any posting in this group; apologies, if this has already been asked.

The documentation tells:

"ParallelArray will give the same results as Array, except for side 
effects during the computation."

I use an anonymous function and no variables; DistributeDefinitions, 
SetSharedVariable etc. can not be the cause for the trouble in the 
following toy example:

In[1]:= arrsum = Array[1/Plus[##]&, {3, 3}, {1, 0}, Plus]
Out[1]= 37/10

In[2]:= parrsum = ParallelArray[1/Plus[##]&, {3, 3}, {1, 0}, Plus]
Out[2]= Join[35/12, 47/60]

In[3]:= parrsum /. Join->Plus
Out[3]= 37/10

Is this a bug, a feature or my thick-wittedness? What can be done?

Well, I could use Total[ParallelTable[...],2] but I don't want to.

Thanks in advance,

P.S.: I came across this problem while coding

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