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Help with a possible bug

• To: mathgroup at smc.vnet.net
• Subject: [mg98870] Help with a possible bug
• From: M8R-lj1smh at mailinator.com
• Date: Mon, 20 Apr 2009 19:11:24 -0400 (EDT)

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"]

• Follow-Ups:
  • Re: Help with a possible bug
    • From: Arnoud Buzing <arnoudb@wolfram.com>