On Fri, Dec 19, 2008 at 4:57 AM, Jan Groenewald <j...@aims.ac.za> wrote:
>
...
>
> sage: A=matrix([[1,2],[2,1]]);A
>
> [1 2]
> [2 1]
> sage: eig=A.eigenvectors_right();eig
>
> [(3, [
> (1, 1)
> ], 1), (-1, [
> (1, -1)
> ], 1)]
> sage: v=eig[0][1][0];v
> (1, 1)
> sage: var('t')
> t
> sage: type(v)
> <type 'sage.modules.vector_rational_dense.Vector_rational_dense'>
> sage: type(v*t)
> <type 'sage.modules.free_module_element.FreeModuleElement_generic_dense'>
>
> For instance, I want to subtract v*t from A*v which is not
> possible in sage.
>
> I think this would have worked if v*t was of the type
> sage.modules.vector_rational_dense.Vector_rational_dense
> just like v. I think it should be that type?
>
> sage: A*v-v*t
> ---------------------------------------------------------------------------
> TypeError Traceback (most recent call last)
>
...
>
> A workaround we are using in the meantime:
>
> sage: A*v-v*identity_matrix(2)*t
> (3 - t, 3 - t)
>
I'm not sure this is a bug or a missing feature or what but here is
another workaround:
sage: t^0*A*v-t*v
(3 - t, 3 - t)
> I still don't get it though, the v*identity_matrix(2)*t has the same type as
> v*t, why
> does that even work as a workaround?
>
> sage: type(v*t)
> <type 'sage.modules.free_module_element.FreeModuleElement_generic_dense'>
> sage: type(v*identity_matrix(2)*t)
> <type 'sage.modules.free_module_element.FreeModuleElement_generic_dense'>
> sage: type(A*v)
> <type 'sage.modules.vector_rational_dense.Vector_rational_dense'>
> sage: type(A*v-v*identity_matrix(2)*t)
> <type 'sage.modules.free_module_element.FreeModuleElement_generic_dense'>
>
> I hope that is clearer.
>
> regards,
> Jan
>
> >
>
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