to_standard modifies the original permutation

[kcrisman]

See this sage-devel thread for several nasty things that happen because combinat methods mess with the lists involved.

sage: from sage.combinat.permutation import to_standard as pts 
sage: a = [1,2,4] 
sage: pts(a) 
[1, 2, 3] 
sage: a 
[5, 5, 5] 
sage: pts([1,1,3]) 
[1, 2, 3] 

Volker Braun also points out

sage: Permutation([3,2])  # invalid one-line notation 
[3, 2] 
sage: _.cycle_string() 
<boom>

CC: @nthiery @hivert

Component: combinatorics

Author: Travis Scrimshaw

Reviewer: Mike Hansen

Merged: sage-5.3.rc0

Issue created by migration from https://trac.sagemath.org/ticket/11425

[tscrim]

Attachment: trac_11425-perm_to_standard_fix-ts.patch.gz

[tscrim]

Author: Travis Scrimshaw

[tscrim]

comment:1

Now it makes a copy of the list and modifies that copy.

The second issue should be handled by #8392 since an invalid permutation is passed in.

[mwhansen]

comment:2

Looks good to me.

[mwhansen]

Reviewer: Mike Hansen

[jdemeyer]

Merged: sage-5.3.rc0