#16323: Construction of BIBD with k=5
-------------------------------------+-------------------------------------
Reporter: ncohen | Owner:
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-6.3
Component: combinatorial | Resolution:
designs | Merged in:
Keywords: | Reviewers:
Authors: Nathann Cohen | Work issues:
Report Upstream: N/A | Commit:
Branch: u/ncohen/16323 | 07a31304b9d48ef6e07f1dd96c1d3185b8fafc95
Dependencies: #16279 | Stopgaps:
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Comment (by ncohen):
Yooooooooo !!
> Perhaps not everything for that ticket but I would like to discuss
several points.
Thanks for reading it, though !
> 1) `BalancedIncompleteBlockDesign` is upper case whereas we start to
agree on lower case would be for "build me one if you know how to" and
!CamelCase would be for "build me this precise design". Should I open a
ticket for that ?
Ahahahah... Yes, probably... `:-)`
> 2) BIBD errors are not smart (compared to TD/OA/MOLS)
> {{{
> sage: designs.BalancedIncompleteBlockDesign(5,6)
> ...
> ValueError: No such design exists !
> sage: designs.BalancedIncompleteBlockDesign(1,6)
> ...
> RuntimeError: maximum recursion depth exceeded while calling a Python
object
> sage: D=designs.BalancedIncompleteBlockDesign(1,5)
> ...
> EmptySetError: No Transversal Design exists when k>=n+2 if n>=2
> }}}
Well, the first one is correct, I am pretty sure I fixed the second
somewhere but let's fix it again here, and the third one is really a
mistake. I will write a ticket for the last two bugs in a second
> 3) It would be nice to have `BIBD_from_difference_family` as a public
function as it
> may serve other purposes. Moreover, the {{{G(x if some_reason else
[x])}}} is
> ugly. I know it is because of `AdditiveAbelianGroup` but it is ugly.
Yes. But you know, it REALLY is because of `AdditiveAbelianGroup` ! Anyway
now we have real cartesian products, I will use that.
> There are
> ways to avoid that (e.g. use `Zmod` for cyclic groups instead of
> `AdditiveAbelianGroup`). For that particular point, I do have
implementation that smooth everything in u/vdelecroix/16323.
Oh... But Zmod is ugly too, because you have to change the way you think
of the code.. We can use cartesian products now that we have them !
> 4) More generally, there are recursive strategies to build difference
family and
> difference matrices... it would be nice to have functions
> {{{
> def difference_family(G, k, l=1, existence=False):
> r"""
> Return a (G,k,l)-difference family if we know how to...
> """
>
> def difference_matrix(G, k, l=1, existence=False):
> r"""
> Return a (G,k,l)-difference matrix if we know how to...
> """"
> }}}
> And moreover, such function might be used to simplify the database.
I know nothing about ways to build difference families and differences
matrices.
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/16323#comment:9>
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