The implementation in sage/modules/vector_symbolic_dense just inherits from
FreeModuleElement_generic_dense, without overriding any methods like _add_
or _new_c. In particular, the arithmetic operations
in FreeModuleElement_generic_dense hard-code the class, so that arithmetic
always creates a new FreeModuleElement_generic_dense (as you're seeing).
The simplest solution may be to change
cdef _new_c(self, object v):
# Create a new dense free module element with minimal overhead and
# no type checking.
cdef FreeModuleElement_generic_dense x
x = PY_NEW(FreeModuleElement_generic_dense)
in FreeModuleElement_generic_dense to
cdef _new_c(self, object v):
# Create a new dense free module element with minimal overhead and
# no type checking.
cdef FreeModuleElement_generic_dense x
x = <FreeModuleElement_generic_dense>PY_NEW(<object>PY_TYPE(self))
David
On Sat, Jun 25, 2011 at 13:56, Joris Vankerschaver <
joris.vankerscha...@gmail.com> wrote:
> Dear all,
>
> I'm playing around with #11335 which was included in Sage
> 4.7.1.alpha3. In this patch, I added a symbolic vector class, with
> the aim of providing simplification methods that act elementwise on
> symbolic vectors. The symbolic vector class derives from
> sage.modules.free_module_element.FreeModuleElement_generic_dense and
> so far only provides methods for simplification, so it's pretty
> simple.
>
> However, it looks like this simple design is not sufficient to ensure
> that the result of simple arithmetic operators stays in the same
> vector space:
>
> sage: v = vector(SR, [1])
> sage: w = vector(SR, [x])
> sage: type(v)
> <class 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
> sage: type(w)
> <class 'sage.modules.vector_symbolic_dense.Vector_symbolic_dense'>
> sage: type(v + w)
> <type
> 'sage.modules.free_module_element.FreeModuleElement_generic_dense'>
>
> I have no idea what the matter is, though. The coercion model reports
> that arithmetic should be performed directly:
>
> sage: cm = sage.structure.element.get_coercion_model()
> sage: cm.explain(v, w, operator.add)
> Identical parents, arithmetic performed immediately.
> Result lives in Vector space of dimension 1 over Symbolic Ring
> Vector space of dimension 1 over Symbolic Ring
>
> Any idea where things went wrong?
>
> Thanks!
> Joris
>
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