Two questions about libgap

[Jesús Torrado]

Dear all,

I have implemented a finite matrix group as explained in "http://www.sagemath.org/doc/reference/sage/groups/libgap_wrapper.html", starting from some matrix generators, i.e. in the example "libgap.Group(generators)" instead of "libgap.CyclicGroup(3)". Everything works fine: I call an element and get its matrix representation printed. However, I can not get the element easily as a Matrix instance, what I want to do to take its Smith normal form. The only way I have found to work so far is, being ``element`` an instance of the Element class,

     sage: Matrix(self.base_ring(), self.gap().sage())

which works, but something tells me there is an easier way. Is there?

Second, how do I cast a gap integer into a safe integer? For example, the following fails:

    sage: a =libgap.DimensionOfMatrixGroup(group)
    sage: print a
    >>> 2
    sage: ZZ(a)
    >>>   [...] TypeError: unable to coerce <type 'sage.libs.gap.element.GapElement_Integer'> to an integer

Is there a proper way, or a workaround?

Anyway, I think libgap is one of the best contributions to sage possible. Thanks so much, Volker!

Cheers,
Jesús Torrado

[Jesús Torrado]

Ok, forget about the 2nd one, sorry: as easy as

    sage a.sage()

Cheers,
Jesús Torrado

[Volker Braun]

I'm working on porting the matrix groups in Sage to libGAP currently. Its not finished yet, but real soon (TM) you'll be able to convert matrices between sage and GAP:

sage: M_s = random_matrix(GF(5), 3)

sage: M_s

[2 0 1]

[3 3 4]

[1 1 1]

sage: type(M_s)

sage.matrix.matrix_modn_dense_float.Matrix_modn_dense_float

sage: M_g = libgap.matrix(M_s)

sage: M_g

[ [ Z(5), 0*Z(5), Z(5)^0 ], [ Z(5)^3, Z(5)^3, Z(5)^2 ], [ Z(5)^0, Z(5)^0, Z(5)^0 ] ]

sage: type(M_g)

sage.libs.gap.element.GapElement_List

sage: MatrixGroup([M_s])

Matrix group over Finite Field of size 5 with 1 generators (

[2 0 1]

[3 3 4]

[1 1 1]

)

sage: _.cardinality()

124

[Jesús Torrado]

Hey,

On Thursday, February 28, 2013 7:13:17 PM UTC+1, Volker Braun wrote:

I'm working on porting the matrix groups in Sage to libGAP currently. Its not finished yet, but real soon (TM) you'll be able to convert matrices between sage and GAP:

Cool! I imagined so. As soon as it is finished, I will incorporate it, but right now, I'll keep my dirty hack.

Thanks again!
Jesús Torrado

[Volker Braun]

Patch is now up at 

http://trac.sagemath.org/14014

[Jesús Torrado]

Great! I will try to test it during the weekend.