Implement the conjugate of a set partition

[zabrocki]

Implement the notion of the conjugate of a set partition defined in "On Conjugates for Set Partitions and Integer Compositions" by David Callan for the combinatorial class SetPartition

[zabrocki]

New commits:

​cc4efc2

initial version and reference

[chapoton]

too late, but this is a bit ugly

if len(initials)+len(singletons)==0:

and could have been

if not initials and not singletons:

[slelievre]

It might be fine to reopen; otherwise fix it in a follow-up ticket.

Along with pep8 and maybe these other small things:

-            return (support+[support[0]])[support.index(a)+1]
+            return support[(support.index(a)+1) % len(support)]

-            support = sorted([a for S in sp for a in S])
+            support = sorted(a for S in sp for a in S)

-        support = sorted([a for S in self for a in S])
+        support = sorted(a for S in self for a in S)

[git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

​6ce6f9e

changed as per comments

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​1cef639

pep8 changes

[aschilling]

Actually, this corner case also needs to be fixed:

    sage: s = SetPartitions(0).list()[0]                                                                                                                                
    sage: s.conjugate()                                                                                                                                                 
    ---------------------------------------------------------------------------
    ValueError                                Traceback (most recent call last)

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​5e86a5b

catch corner case

[aschilling]

Add a doc test to the corner cases too!

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​7e6a9ec

add doc test for corner case

[slelievre]

Frédéric, any final formatting touch?

Then back to positive review?

[aschilling]

Yes, you can set it back to positive review!