Janko Groups and Livingstone graph

[ncohen]

This branch exposes the Janko groups from gap, and builds the Livingstone Graph from J1

​https://en.wikipedia.org/wiki/Janko_group ​https://en.wikipedia.org/wiki/Livingstone_graph

Nathann

[ncohen]

New commits:

​42e61b8

trac #18774: Livingstone Graph and Janko Groups

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​8b7160a

trac #18774: Livingstone Graph and Janko Groups

[dimpase]

JankoGroup(4) should throw NotImplementedError; I don't think anyone wants a permutation group of degree 173067389, and they aren't known by AtlasRep, as far as I know (IMHO they have the same data as in ​http://brauer.maths.qmul.ac.uk/Atlas/v3/spor/J4/).

gap> i:=AtlasGroup("J4");
<matrix group of size 86775571046077562880 with 2 generators>

while for the remaining values of k<4 you get

gap> i:=AtlasGroup("Jk");
<permutation group of size ....... with 2 generators>

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​7efe54b

trac #18774: no J4

[ncohen]

Hello,

JankoGroup(4) should throw NotImplementedError;

Right, right. I simplified it and requested an integer from 1 to 3 instead.

Nathann

[chapoton]

tests do not pass

shouldn't this be tagged optional - gap_something ?

[ncohen]

shouldn't this be tagged optional - gap_something ?

HMmm... Gap isn't optional. And with gap installed on my computer, I did not notice that an optional package was needed ^^;

I don't even know which package is needed O_o

Nathann

[dimpase]

you need internet access to use AtlasRep? in GAP. I also think that AtlasRep? comes in gap_packages, i.e. is optional.

(I'm currently travelling, so please excuse my non-constant attention)

[ncohen]

Hellooooo !

you need internet access to use AtlasRep? in GAP.

Whaaaaaaaaat ? I'll check this immediately.

I also think that AtlasRep? comes in gap_packages, i.e. is optional.

Yep. It is inside.

Nathann

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​93801c8

trac #18774: optional gap packages

[ncohen]

It works offline, but gap_packages must be installed.

[dimpase]

Replying to ncohen:

It works offline,

Really? ​http://www.math.rwth-aachen.de/~Thomas.Breuer/atlasrep/ (the official www-pages of the package) says

 Note that the package archives do NOT contain the database part of the package; the GAP interface accesses the data on demand via the internet.

[ncohen]

Really?

I built if offline. You think that they have a caching mechanism for that, between sessions?...

Nathann

[dimpase]

Replying to ncohen:

Really?

I built if offline. You think that they have a caching mechanism for that, between sessions?...

of course you can build it offline, but not use offline (although perhaps some of its data is in other GAP databases).

perhaps one has to read its code...

Nathann

[dimpase]

TFM says:

4.3 User Parameters for the AtlasRep Package

This section lists global parameters for which it might make sense to change their defaults by assignments to global variables, either just for the current GAP session or as user preferences in the user's gaprc file (see Reference: The gap.ini and gaprc files). For an overview of these parameters, see AtlasOfGroupRepresentationsUserParameters (4.3-8).

4.3-1 Local or Remote Access

There are two possibilities to use the AtlasRep package.

Local access only (offline)

    You can restrict the access to the data that are actually stored in the local installation of GAP.
Remote access (online)

    If your computer is connected to a network that provides access to the ATLAS data (for example the internet) then the functions of the package may fetch the requested data automatically from remote servers when they are required for the first time; these data are then by default stored in the local copy, so later access to them needs no network transfer.

The latter possibility is presently not used by other GAP packages, so it may be regarded as an important feature of the AtlasRep package. Anyhow it requires a few words of explanation.
...

[ncohen]

I just did the following:

• Went offline
• 'sage -f gap_packages'
• 'rm -rf ~/.sage/gap/'
• 'make'
• 'sage -br'

sage: graphs.LivingstoneGraph()
Livingstone Graph: Graph on 266 vertices

So for the moment, I will keep on believing that this works offline. Unless you know where it could be cached?

Nathann

[dimpase]

Replying to ncohen:

So for the moment, I will keep on believing that this works offline. Unless you know where it could be cached?

RTFM?

Then, there is stuff in $SAGE_LOCAL/gap

[ncohen]

RTFM?

Always a pleasure to work with you dima.

Then, there is stuff in $SAGE_LOCAL/gap

Yeah, I just figured this out offline. The thing is that you are not supposed to have writing access to SAGE_LOCAL/gap, so that's not precisely where cached information should be stored. It should be done in ~/.sage/gap

Anyway, this requires internet indeed.

Nathann

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​2548e0e

trac #18774: internet

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​e977c17

trac #18774: internet

[dimpase]

Replying to ncohen:

RTFM?

Always a pleasure to work with you dima

as we know, it's just an abbreviation of "Highly respected colleague, allow me most humbly point to availability of material that might alleviate doubts you have hinted at in your most valuable comments above"

:-)

[ncohen]

as we know, it's just an abbreviation of [...]

I see. My life so far has been a lie.

Nathann

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​d07e879

say why J4 is not there

[dimpase]

Nathann, LGTM. Feel free to flip it to positive review if you're happy with my last commit.

[dimpase]

Replying to ncohen:

Then, there is stuff in $SAGE_LOCAL/gap

Yeah, I just figured this out offline. The thing is that you are not supposed to have writing access to SAGE_LOCAL/gap, so no information should be cached there. It should be done in ~/.sage/gap

so is there (where?) a bug?

[ncohen]

so is there (where?) a bug?

Not sure. They may write to the system-wide repository if they can, and if they cannot then they write to the home gap directory.

[ncohen]

LGTM. Feel free to flip it to positive review if you're happy with my last commit.

Works for me. Thanks!

Nathann