#16534: Basic Block design methods
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Reporter: brett | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.4
Component: combinatorial | Resolution:
designs | Merged in:
Keywords: Block Design, | Reviewers:
Incidence Structure, Residual, | Work issues:
Derived, Complement, Supplement, | Commit:
Point Deletion | f72a8ed01c5745f16f8f1bb317cd5e81d6cf6584
Authors: Brett Stevens | Stopgaps:
Report Upstream: N/A |
Branch: u/brett/design |
Dependencies: #16553 |
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Comment (by ncohen):
Hello,
> sure, in any particular order?
As you see fit. I would say 'respect the alphabetical order' if the
existing entries do, otherwise reorder them, otherwise add them to the end
of the list, otherwise [...].
> You mean in the other functions I will see how to have the same
functionality without the waste of time and space?
Indeed.
> way back when I started these methods, the blocks were not sorted and
this led to __eq__ not working properly, so I do this to makes sure that
everything is in a invarient form.
Oh I see. Well, this has been solved some time ago and you do not have to
sort the blocks anymore. You can, optionally, give the blocks to
`IncidenceStructure` and 'swear' that they are already sorted: this is
only useful to save some time when you know that the blocks are already as
they should.
> In design theory when we delete points we keep the blocks that had the
point, we just remove the points from them. This is like truncating a
group in a TD (you keep the group) or going from projective plane to the
affine plane it contains (you keep all the lines, except the one which
ends up empty). I don't mind this doing this inplace like the graphs.
Well, doing this inplace raises new problems: you cannot do that in an
object of type `BIBD` as it will not remain a `BIBD` (most of the time).
We are somehow stuck there, which is why I proposed this optional argument
to `trace/induced_substructure`.
Cheers,
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/16534#comment:17>
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