#19038: Better hash on FPGroups
-----------------------+----------------------------
Reporter: nbruin | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.9
Component: algebra | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
-----------------------+----------------------------
As is pointed out on #19016 the hash on FPGroup elements is currently
based on the (non-canonical) representation, whereas the equality test is
a more elaborate one borrowed from Gap. That means currently, there are
elements that are equal but have different hashes
{{{
sage: G.<a,b>=FreeGroup()
sage: Q=G.quotient([a*b])
sage: U=Q(a)*Q(b)
sage: V=Q(1)
sage: U==V
True
sage: hash(U)==hash(V)
False
}}}
When Gap does succeed in testing equality, it does so via a normal form of
its elements. One way of equipping FPGroups with a well-behaved hash is by
getting that normal form from gap and hash that.
--
Ticket URL: <http://trac.sagemath.org/ticket/19038>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/d/optout.
