# Calculate Right Cosets

How do I get sage to list the right cosets for the group G = GL2(F3) and the subgroup H consisting of the upper triangular matrices with 1 on the main diagonal?

Calculate Right Cosets

asked
**
2011-03-25 11:58:22 -0500
**

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How do I get sage to list the right cosets for the group G = GL2(F3) and the subgroup H consisting of the upper triangular matrices with 1 on the main diagonal?

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answered
**
2011-03-26 07:07:48 -0500
**

This post is a wiki. Anyone with karma >750 is welcome to improve it.

You can construct `GL(2, F3)`

in Sage using:

```
G=GL(2,GF(3))
```

See the reference manual for more about what you can do with a general linear group in Sage:

http://www.sagemath.org/doc/reference/sage/groups/matrix_gps/general_linear.html

As for cosets in Sage, some groups have this implemented, like the permutation groups:

```
H = PermutationGroup([(1,2),(1,2,3)])
P = H.subgroup([(2,3)])
H.cosets(P, side='right')
[[(), (2,3)], [(1,2), (1,2,3)], [(1,3,2), (1,3)]
```

But this isn't implemented directly in Sage for groups like the general linear group over a finite field. You could input `GL(2, F3)`

into Sage as a permutation group (this is a good exercise perhaps) and use the `cosets`

method.

```
%gap
# define general linear group
G := GL(2,3);;
P := NiceObject(G);
Print(P,"\n");
# define upper triangular subgroup
g1 := [[Z(3),0*Z(3)],[0*Z(3),Z(3)]];;
g2 := [[Z(3),Z(3)],[0*Z(3),Z(3)]];;
M := Group(g1,g2);;
MP := NiceObject(M);
Print(MP);
Group( [ (4,7)(5,8)(6,9), (2,7,6)(3,4,8) ] )
Group( [ (2,3)(4,7)(5,9)(6,8), (2,3)(4,9,6,7,5,8) ] )
```

Then in Sage:

```
G = PermutationGroup([ [(4,7),(5,8),(6,9)], [(2,7,6),(3,4,8)] ])
H = G.subgroup( [[(2,3),(4,7),(5,9),(6,8)], [(2,3),(4,9,6,7,5,8)]] )
G.cosets(H, side='right')
```

Of course you could do all of that directly in GAP (through Sage or not) if you want and it will be much faster for larger groups.

Asked: **
2011-03-25 11:58:22 -0500
**

Seen: **1,083 times**

Last updated: **Mar 26 '11**

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