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strongly regular tournaments #24682

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dimpase opened this issue Feb 7, 2018 · 11 comments · Fixed by #34986
Closed

strongly regular tournaments #24682

dimpase opened this issue Feb 7, 2018 · 11 comments · Fixed by #34986
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c: graph theory p: major / 3 t: enhancement

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@dimpase
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dimpase commented Feb 7, 2018 •
edited by mkoeppe
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This is a followup to #24045:

This is generalisation of Paley digraphs from #24045, due to A.Duval, ​J.Comb.Th. 47(1988) pp. 71-100, nowadays called strongly regular digraph/tournament. We can use code in comment 14 of #24045, and Paley would be a subcase (in fact, this code will give you Paley if 4n-1 happens to be a prime power).

Component: graph theory

Author: Matteo Cati

Issue created by migration from https://trac.sagemath.org/ticket/24682
@dimpase dimpase added this to the sage-8.2 milestone Feb 7, 2018
@mkoeppe mkoeppe removed this from the sage-8.2 milestone Dec 29, 2022
@MatteoCati
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Author: Matteo Cati

@MatteoCati
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Commit: 4cd5664

@MatteoCati
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New commits:

4cd5664Add construction of strongly regular digraph

@MatteoCati
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Branch: u/gh-MatteoCati/add_strongly_regular_digraph

@dcoudert
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comment:3

You assume the existence of a unique strongly regular digraph of order n. Is it the case ?

  • n+1 -> n + 1
  • f'Strongly regular digraph' -> 'Strongly regular digraph'

@dimpase
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dimpase commented Jan 30, 2023

comment:4

no, they are usually not unique (IIRC, already for 19 nodes it's not the case)

@dimpase
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dimpase commented Jan 30, 2023

comment:5

But where do you see a uniqueness promise? The docs say

Return a Strongly Regular digraph with `n` vertices.`

@dcoudert
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comment:6

I haven't seen any promise on the uniqueness. I just observed that the construction always returns the same digraph of order n.
You could add in the documentation for future work to add other constructions.

@dimpase
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dimpase commented Jan 30, 2023

comment:7

yes, it's the same for many other combinatorics and graphs constructions.
E.g. if you ask for a Hadamard matrix of order n you get the 1st found, or if you ask got a strongly regular graph with the given parameters you get the 1st founds, same for block designs, orthogonal arrays, etc.

(the trac is read-only for all, except me, now, we'll get back to this on GitHub :-))

@dimpase
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dimpase commented Jan 30, 2023

comment:8

test+1

@MatteoCati MatteoCati mentioned this issue Feb 6, 2023
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@mkoeppe
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mkoeppe commented Feb 12, 2023

Removed branch from the issue description because it has been replaced by PR #34986

vbraun pushed a commit that referenced this issue Feb 19, 2023
gh-pr-34986: Add construction of strongly regular digraph
08185d7 
Fixes #24682.

URL: #34986
Reported by: MatteoCati
Reviewer(s): David Coudert
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Add construction of strongly regular digraph MatteoCati/sage
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@dimpase @mkoeppe @dcoudert @MatteoCati