Hi Marco,
On 11 Jan., 13:30, Marco Streng <[email protected]> wrote:
> I'm not sure what you mean by ``making the coercion model use containers
> that compare by "is" and not by "=="'',
If you have a dictionary D with keys A and B such that "A==B" but "A
is not B", then you will always have "D[A] is D[B]" -- of course
unless you screw that hash functions of A and B, which currently is
the case for matrix spaces. This is simply how Python dictionaries
work.
However, sage.structure.coerce_dict.TripleDict has the property that
(1) each key is a triple and (2) the three parts of the key are
compared by identity and not by equality. Hence, "D[A,A,A] is not
D[A,B,A]".
> but I'll just chime in as I
> think it could be related to something that I found.
The topic is certainly (weakly, at least :) related.
> sage: K.<a> = NumberField(x^2-2, embedding=-1)
> sage: L.<b> = NumberField(x^2-2, embedding=1)
> sage: xK = K['x'].gen()
> sage: xL = L['x'].gen()
> sage: M.<c> = NumberField(xK^2-3)
> sage: N.<d> = NumberField(xL^2-3)
> sage: O = M.absolute_field('e')
> sage: P = N.absolute_field('e')
Yep, non-uniqueness strikes again:
sage: O==P
True
sage: O is P
False
But I think in this case there should be other ways to ensure that the
conversion from O to P is really just used as conversion and not as
coercion.
Cheers,
Simon
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