#10527: Implementation of quiver mutation type
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Reporter: stumpc5 | Owner: sage-combinat
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.3
Component: combinatorics | Resolution:
Keywords: quiver mutation type days38 | Work issues:
Report Upstream: N/A | Reviewers: Hugh Thomas
Authors: Christian Stump | Merged in:
Dependencies: | Stopgaps:
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Comment (by hthomas):
Yay! So far as I can tell, the only complaint the patchbot is making is
that we're adding new modules, but since we're importing them lazily, it's
not really a problem.
I had never reviewed Gregg's final patch. I've now looked at it and I'm
afraid I have some minor issues with it. (And testing it has led to
detecting some other non-optimal behaviour.)
Gregg, you said you wanted to fix !QuiverMutationType('C',1,1) giving a
cryptic message, but in fact it still does (it still says "'CC',1,1" is
not valid).
I see you changed the error message to reflect the fact that in elliptic
types, twists can have 2's in them, which is better than what was there
before. But they can also have 3's in them (elliptic G's).
In fact, I suggest removing the last four lines of the error message,
including the elliptics, and replacing them by "For correct syntax in
other types, please consult the documentation." As it stands, it looks
like it's purporting to be some kind of complete list, but in fact not
every type is well-described (e.g., GR, which takes a single additional
parameter which is a tuple/list blah, blah). In general, I don't think
the goal of an error message should be to replace the documentation.
I still think it's pointless to include AE. If you want it, it definitely
shouldn't have a twist of 3. And I think the documentation should explain
the input format.
I'm not sure why we're allowing !QuiverMutationType('GR',(n,k)) as well as
(k,n). The Grassmannian of 3-planes in 2-space is just meaningless, and
(in my view) it should return an error. I could be argued out of this.
!QuiverMutationType('D',3,2) works, but !QuiverMutationType('A',3,2)
doesn't. But A_3 and D_3 are the same. I think both should yield what
D,3,2 does now (namely, C,2,-1). There has to be some notation for it,
and it's pretty peculiar to require people to think of the root system as
derived from D,3 rather than A,3. (The reason this makes some sense is
that it fits the pattern of D,n,2, not the pattern of A,2n+1,2, but I
think that's okay.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10527#comment:113>
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