**diff options**

author | Release Manager <release@sagemath.org> | 2015-08-05 12:52:22 +0200 |
---|---|---|

committer | Volker Braun <vbraun.name@gmail.com> | 2015-08-05 12:52:22 +0200 |

commit | 1b01a852c389bf9959e552e0e90efbf3153a30a9 (patch) | |

tree | ed8a25c39da0d992832e6a6c634bd3f7683121c3 | |

parent | Trac #18989: Incorrect input_alphabet in FiniteStateMachine.disjoint_union (diff) | |

parent | trac #18948: Broken doctest (diff) |

Trac #18948: Strongly Regular Graphs database

This ticket implements a new module names `strongly_regular_db` that
lets us build one example of strongly regular graph, given four integer
parametes (v,k,lambda,mu).
It uses Andries Brouwer's database to return more meaningful non-
existence results, and help us find which constructions are missing from
the database.
With a bit of luck (and time, and work) it would be great if we could
reproduce all SRG that are known to exist!
The module has a simple structure:
has a simple structure:
- A `seems_feasible(v,k,l,mu)` function that performs the basic
artihmetic
checks to figure out if `(v,k,l,mu)` is realizable. The
'apparently_feasible_parameters(n)` returns the lists of all
parameters that
pass these tests for v<n. When n=1301, the set of parameters it
returns is
precisely those that appear on your database (this is checked in the
code).
- Several functions (is_paley, is_johnson, ...) test if a given set of
parameters (v,k,l,mu) can be realized with a graph of the
corresponding family
(a Paley graph, a Johnson graph, ...). If they can, they return the
parameters
of that graph so that it can be built easily.
- The main function `strongly_regular_graph` can be called in two ways:
- `strongly_regular_graph(v,k,l,mu,existence=True)` answers True if
such a
graph is known to exists, False if it is known to be infeasible, and
Unknown
otherwise.
- `strongly_regular_graph(v,k,l,mu)` attempts to build and return the
requested graph, and returns a meaningful exception if it cannot.
This branch also updates the package 'graphs', which now ships the
database in json format.
http://www.steinertriples.fr/ncohen/tmp/graphs-20150724.tar.bz2
Nathann
URL: http://trac.sagemath.org/18948
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Dima Pasechnik

-rw-r--r-- | build/pkgs/graphs/SPKG.txt | 16 | ||||

-rw-r--r-- | build/pkgs/graphs/checksums.ini | 6 | ||||

-rw-r--r-- |