Baffling behavior of Factor[] in versions 5 and 6 -- a bug?

*To*: mathgroup at smc.vnet.net*Subject*: [mg82375] Baffling behavior of Factor[] in versions 5 and 6 -- a bug?*From*: sbonano at inp.demokritos.gr*Date*: Thu, 18 Oct 2007 05:05:23 -0400 (EDT)

Hello, I have encountered the following strange behavior in applying Factor to expressions that are already factored: expr[n_]:=(1 + CC(t^2 - x^2 - y^2))^n(1 - CC(u^2 + v^2 + w^2))^n timeTest[n_]:= Transpose[{Factor[expr[n]]// Timing, Factor[expr[-n]]//Timing}][[1]] timeTest[3] {0. Second, 1.15 Second} timeTest[4] {0.01 Second, 14.64 Second} Factor takes an unacceptably long time when n is negative (try timeTest[5]!). This behavior did not exist in versions <5. I consider it a bug. The following modification of Factor behaves as one would expect myFactor[x_]:=If[Head[x] === Times, Times@@Factor[List@@x], Factor[x]] Shouldn't such a line be part of the definition of Factor, when no Extensions have been specified? S. Bonanos http://www.inp.demokritos.gr/~sbonano/ PS The factors in expr are the conformal factors of two constant-curvature 3-dimensional spaces (coordinates {t,x,y} and {u,v,w} respectively). I discovered this bug when my RGTC program (http://www.inp.demokritos.gr/~sbonano/RGTC/) was unable to calculate the inverse of the 6-dimensional metric which is the direct sum of these two 3-d metrics -- it got stuck factoring expr[-6]! -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.

**Follow-Ups**:**Re: Baffling behavior of Factor[] in versions 5 and 6 --***From:*Daniel Lichtblau <danl@wolfram.com>