MathAction #295 PERM movedPoints wrong

Topics

movedPoints$Permutation computes the set of moved points incorrectly:

fricas

(1) -> p := coerceImages([1,2,3])$PERM INT

$\label{eq1}1$

Type: Permutation(Integer)

fricas

movedPoints p

$\label{eq2}\left\{ \right\}$

Type: Set(Integer)

Note that p really is the identity permutation, so the set of moved points should be empty...

This bug was obviously known to the original authors, we read:

      movedPoints p == construct p.1  --check on fixed points !!

but they never bothered to fix it. In the line above, p.1 simply is the preimage of the permutation p, so there are two ways to fix the bug:

remove fixed points from preimage and image, always when permutations are generated
check on fixed points only in movedPoints

This patch chooses the first option, which seems to be also what the original authors had in mind.

Martin

... --kratt6, Sat, 03 Jun 2006 12:50:45 -0500 reply

Unfortunately, MathAction doesn't seem to like my patch: I can't upload it. Well it's on the mailing list anyway...

Martin

patch uploaded --billpage, Sat, 03 Jun 2006 16:03:21 -0500 reply

The previous attempt to upload failed because of some over active anti-spam checking. It works now.

fixed in Patch 50 --kratt6, Fri, 27 Oct 2006 03:06:56 -0500 reply

Status: open => closed