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Re: Help with a possible bug

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98928] Re: Help with a possible bug
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Wed, 22 Apr 2009 05:10:07 -0400 (EDT)
  • References: <gsivea$9bt$1@smc.vnet.net>

M8R-lj1smh at mailinator.com wrote:
> At work we seem to have stumbled on a strange bug between Table and
> Part.  We can reproduce the bug on differently configured Mac and
> Linux boxes.  I tried Wolfram support, but they claim they cannot
> reproduce the bug.  So I was hoping someone could try it out and
> report their results.    Thanks in advance to all volunteers.
> 
> For us, the bug is new in 7.0.1. It does not show up in version 6.
> To reproduce it, fill up a 17 x 267 matrix with 3s.  Compute the sum
> of some of the columns and you get the result 51 (17 x 3).  But if one
> computes the sum for the last few columns, the result is completely
> off.  The bug seems to arise from the interaction of optimizations  in
> Table and the use of All inside of Part.
> 
> 
> ------------  code
> 
>   mat = Table[3, {i, 1, 17}, {j, 1, 267}];
> 
>   sum = Table[Total[mat[[All, j]]], {j, 1, 249}]
> 
>   sum1 = Table[Total[mat[[All, j]]], {j, 1, 252}];
>   sum2 = Table[Total[mat[[All, j]]], {j, 1, 252}]
> 
> ------------  end code
> 
> If you look at sum1, it will be correct on a fresh copy of the
> Kernel.  The problem only arise from the second time on.
> 
> Thanks,
> 
> Papin
> 
> Email: ImportString["cGFwaW5AY294Lm5ldA==", "Base64"]
> 

I can't reproduce the problem in Windows.  I'm just writing to say that 
the magic number 250 appears in some of the system options controlling 
automatic compilation and array packing (see e.g. "TableCompileLength"). 
  You can see or set with SystemOptions[].  Perhaps this information 
will help you work around the problem until it gets fixed.


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