IncidenceStructure.is_uniform, is_regular, and complement

[nathanncohen]

Three methods that we miss. One of them seems to be useful for #18972.

I have been trying to find a way for those methods to tell you at the same time if a hypergraph is k uniform, and the value of k. There is an unfortunate corner-case, but I still think that it is the best way to implement it.

Nathann

CC: @dimpase @videlec

Component: combinatorial designs

Author: Nathann Cohen

Branch/Commit: 55f934b

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/18986

[nathanncohen]

Commit: 55f934b

[nathanncohen]

Branch: u/ncohen/18986

[nathanncohen]

New commits:

55f934b

trac #18986: IncidenceStructure.is_uniform, is_regular, and complement

[dimpase]

comment:2

LGTM

[dimpase]

Reviewer: Dima Pasechnik

[dimpase]

comment:3

How would I use complement in #1897 ? I need it to be called with uniform=True. How does one write this:

def complement(): # not actual code
    return self.???inherited???.complement(uniform=True)

thanks,
Dima

[dimpase]

comment:4

I tried

   def complement(self):
        return super(self).complement(uniform=True)

and got

sage: p=graphs.CompleteGraph(8).line_graph().twograph()
sage: p.complement()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-cc3764592501> in <module>()
----> 1 p.complement()

/home/dima/software/sage/local/lib/python2.7/site-packages/sage/combinat/designs/twographs.pyc in complement(self)
    141 #        return TwoGraph(filter(lambda x: not list(x) in self.blocks(),
    142 #                                combinations(self.ground_set(), 3)))
--> 143         return super(self).complement(uniform=True)
    144 
    145 """

TypeError: must be type, not TwoGraph

[dimpase]

comment:5

Replying to @dimpase:

I tried

   def complement(self):
        return super(self).complement(uniform=True)

and got

sage: p=graphs.CompleteGraph(8).line_graph().twograph()
sage: p.complement()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-cc3764592501> in <module>()
----> 1 p.complement()

/home/dima/software/sage/local/lib/python2.7/site-packages/sage/combinat/designs/twographs.pyc in complement(self)
    141 #        return TwoGraph(filter(lambda x: not list(x) in self.blocks(),
    142 #                                combinations(self.ground_set(), 3)))
--> 143         return super(self).complement(uniform=True)
    144 
    145 """

TypeError: must be type, not TwoGraph

Oh, I see, it must be super(TwoGraph,self). Then it works, OK, question answered, sorry for noise.

[vbraun]

Changed branch from u/ncohen/18986 to 55f934b