Re: [sage-devel] submodules subvectorspaces violate the unique parent condition. Why? Should we change that?
The reason why unique parents were introduced is for speed and memory reasons. Having a million copies of the same parent around is a bit of a waste, but this is something that happens quite easily if one does not make parents unique. I also noticed that submodules violate the "equal => equal hash principle" since: X = QQ^2 V = X.span([[1,0],[0,1]]) W = X.span_of_basis([[1,0],[0,1]]) Are all equal but have distinct hashes. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
Re: [sage-devel] submodules subvectorspaces violate the unique parent condition. Why? Should we change that?
"While *parents* are unique, equal *elements* of a parent in Sage are not
necessarily identical. "
in
http://doc.sagemath.org/html/en/tutorial/tour_coercion.html
OK. In the parent class it says
"...this is useful if parents are unique, or element_constructor is a bound
method (this latter case can be detected automatically). ..."
So uniqueness is not strict. But when is a parent supposed to be unique and
when not?
On Monday, October 9, 2017 at 9:48:29 AM UTC+2, vdelecroix wrote:
>
> It is a violation of what!? Where did you read that parents should be
> unique?
>
> On 09/10/2017 09:26, Simon Brandhorst wrote:
> > {{{
> > sage: V = span(QQ,[(1,1),(1,0)])
> > sage: W = span(QQ,[(0,1),(1,0)])
> > sage: V
> >
> > Vector space of degree 2 and dimension 2 over Rational Field
> > Basis matrix:
> > [1 0]
> > [0 1]
> > sage: W
> >
> > Vector space of degree 2 and dimension 2 over Rational Field
> > Basis matrix:
> > [1 0]
> > [0 1]
> > sage: V is W
> > False
> > sage: V==W
> > True
> > sage: type(V)
> > 'sage.modules.free_module.FreeModule_submodule_field_with_category'>
> > sage: type(W)
> > 'sage.modules.free_module.FreeModule_submodule_field_with_category'>
> > }}}
> >
> > They are parents. Yet they are not unique.
> >
>
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Re: [sage-devel] submodules subvectorspaces violate the unique parent condition. Why? Should we change that?
It is a violation of what!? Where did you read that parents should be
unique?
On 09/10/2017 09:26, Simon Brandhorst wrote:
{{{
sage: V = span(QQ,[(1,1),(1,0)])
sage: W = span(QQ,[(0,1),(1,0)])
sage: V
Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: W
Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: V is W
False
sage: V==W
True
sage: type(V)
sage: type(W)
}}}
They are parents. Yet they are not unique.
--
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[sage-devel] submodules subvectorspaces violate the unique parent condition. Why? Should we change that?
{{{
sage: V = span(QQ,[(1,1),(1,0)])
sage: W = span(QQ,[(0,1),(1,0)])
sage: V
Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: W
Vector space of degree 2 and dimension 2 over Rational Field
Basis matrix:
[1 0]
[0 1]
sage: V is W
False
sage: V==W
True
sage: type(V)
sage: type(W)
}}}
They are parents. Yet they are not unique.
--
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