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MathGroup Archive 1993

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Mma bug

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Mma bug
  • From: Jack K. Cohen <jkc at dix.mines.colorado.edu>
  • Date: Thu, 7 Jan 93 12:36:21 -0700

[Watch for follow up on this issue from WRI. -smc]

The internet is alive with news of a simple expression that
hangs up mma.  I am 99.9% sure that someone from wri must
have picked up the bad news, but just to assure that last .1% ...
                  2
Pi Sqrt[Pi] /(6 Sqrt[2]) //Timing

$IterationLimit::itlim: Iteration limit of 4096 exceeded.
                             3
                           Pi
                      Sqrt[---]
                            8
{49.8833 Second, Hold[---------]}
                          3

The apparent problem is an infinite oscillation between writing
Sqrt[8]  and writing 2 Sqrt[2].  You can replace 2 by 5, 7, ...
and get the same hang up (eg. 10 Sqrt[5] in the denominator).

More complicated expressions don't fall victim to this deadlock and  
undoubtedly that's how this slipped by for so long.  I am sure some  
programmer at wri feels like crawling under a rock today and he/she  
has my sympathy as a fellow hacker.

Jack





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