Opened 3 years ago
Last modified 10 days ago
#28539 needs_work task
Optimization for small permutation groups
Reported by:  vdelecroix  Owned by:  

Priority:  major  Milestone:  
Component:  combinatorics  Keywords:  
Cc:  tscrim, chapoton, sbrandhorst  Merged in:  
Authors:  Vincent Delecroix  Reviewers:  
Report Upstream:  N/A  Work issues:  
Branch:  u/vdelecroix/28539 (Commits, GitHub, GitLab)  Commit:  44bd8638bebbed543ff6f3c13846893ebca17f8b 
Dependencies:  #28544, #28652, #28653  Stopgaps: 
Description (last modified by )
This ticket proposes micro optimizations for small permutation groups. The rationale is to handle the situation where we have billions of combinatorial objects and need to run through their automorphism groups most of which are trivial or let's say have size at most 100. An even more concrete application is given by admcycles MR 14 where there is an attempt to use graph automorphisms from Sage instead of a handmade implementation. This turns out to result in a major slowdown! For example
sage: from admcycles.admcycles import Hyperell sage: %time H = Hyperell(3)
takes 13.5 s on master but with MR 14 takes 17.4 s.
The profiling points to
 the constructor
__init__
ofPermutationGroupElement
: see #28652  the
subgroup
method ofPermutationGroupElement
 the product
p1 * p2
whenp1
is a symmetric group element andp2
is a permutation group on the same domain: see #28652 (and also the bug #28544) __iter__
forPermutationGroupElement
(that currently involves computing a strong generating scheme): see #28652 and #28653
The optimizations proposed in this ticket noticeably speed up
the Hyperell(3)
computation mentioned above: from 17.4 s with
the previous Sage implementation or 13.5 s with admcycle's
previous handmade implementation, the timing goes down to 9 s.
Change History (25)
comment:1 Changed 3 years ago by
Branch:  → u/vdelecroix/28539 

Commit:  → f67ffcc1bcfcd460a6364948e0c875573f31675c 
comment:2 Changed 3 years ago by
Description:  modified (diff) 

comment:3 Changed 3 years ago by
Commit:  f67ffcc1bcfcd460a6364948e0c875573f31675c → 0dbcc3383eac6497c1f7c0711e17b9e831cfeb14 

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:
096659c  28539: rework constructor of PermutationGroupElement

2d23d92  28539: faster multiplication and iteration

d00d370  28539: fix some doctests

5888249  28539: mark not tested bug tracked in #28544

0dbcc33  28539: reynolds operator and Galois conjugation

comment:4 Changed 3 years ago by
Cc:  chapoton sbrandhorst added 

Status:  new → needs_review 
comment:6 Changed 3 years ago by
Commit:  0dbcc3383eac6497c1f7c0711e17b9e831cfeb14 → 6ca3833fff437f52136279a0c6273954f093a8b1 

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:
2c62905  28539: rework constructor of PermutationGroupElement

55d3e8a  28539: faster multiplication and iteration

b027f91  28539: fix some doctests

5d77c23  28539: mark not tested bug tracked in #28544

6ca3833  28539: reynolds operator and Galois conjugation

comment:7 Changed 3 years ago by
Commit:  6ca3833fff437f52136279a0c6273954f093a8b1 → 44bd8638bebbed543ff6f3c13846893ebca17f8b 

Branch pushed to git repo; I updated commit sha1. New commits:
44bd863  28539: fix more doctests (python2 and python3)

comment:8 Changed 3 years ago by
Status:  needs_work → needs_review 

comment:9 Changed 3 years ago by
Still failing. And proliferation of #py2 and # py3 does not seem to be a good solution.
comment:10 Changed 3 years ago by
Status:  needs_review → needs_info 

I agree with Frédéric that adding a whole bunch of # py2
and # py3
tags is not a good solution. I am assuming this comes from this change:
 return self.iteration(algorithm="SGS") + if len(self._gens) == 1: + return self._iteration_monogen() + elif self.cardinality() <= 100: + return self.iteration(algorithm="BFS") + else: + return self.iteration(algorithm="SGS")
and the BFS
option calls RecursivelyEnumeratedSet
, which has consistency problems on Python3 IIRC. So we have to solve that bigger problem first.
I have some other comments:
I don't see the point of going to cycles just to convert back here:
return grp.element_class(self.to_cycles(singletons=False), grp, check=False)
I know this was already done, but it seems useless as the PermutationGroupElement
stores things internally as a list in essentially the same way.
I would probably Cythonize from_cycles
.
Is there a reason why _set_identity
and _set_list_images
are cpdef
and not just cdef
(which is faster when being called by C code)? By being cpdef
, they also need doctests.
comment:11 Changed 3 years ago by
Thanks for the feedback. I will cut the ticket and start by optimizing the constructor. Optimizing the iterator will be postponed to another one.
comment:12 Changed 3 years ago by
Dependencies:  → #28652 

Description:  modified (diff) 
Type:  enhancement → task 
comment:13 Changed 3 years ago by
Dependencies:  #28652 → #28544, #28652, #28653 

Description:  modified (diff) 
comment:14 followup: 15 Changed 3 years ago by
See also #28674 which should eventually solve the consistency problems of RecursivelyEnumeratedSet
.
comment:15 Changed 3 years ago by
Replying to ghmwageringel:
See also #28674 which should eventually solve the consistency problems of
RecursivelyEnumeratedSet
.
I don't think that the enumeration order is relevant here. This is convenient for doctests and only shows the weakness of them.
comment:16 Changed 3 years ago by
Milestone:  sage9.0 → sage9.1 

Ticket retargeted after milestone closed
comment:17 Changed 3 years ago by
Milestone:  sage9.1 → sage9.2 

Batch modifying tickets that will likely not be ready for 9.1, based on a review of the ticket title, branch/review status, and last modification date.
comment:18 Changed 2 years ago by
Description:  modified (diff) 

Status:  needs_info → needs_work 
Supporting Python 2 is no longer needed now.
comment:19 Changed 2 years ago by
Milestone:  sage9.2 → sage9.3 

comment:20 Changed 2 years ago by
Milestone:  sage9.3 → sage9.4 

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.
comment:21 Changed 19 months ago by
Milestone:  sage9.4 → sage9.5 

Setting a new milestone for this ticket based on a cursory review.
comment:22 Changed 14 months ago by
Milestone:  sage9.5 → sage9.6 

comment:23 Changed 10 months ago by
Milestone:  sage9.6 → sage9.7 

comment:24 Changed 5 months ago by
Milestone:  sage9.7 → sage9.8 

comment:25 Changed 10 days ago by
Milestone:  sage9.8 

New commits:
WIP: make small perm group faster