On Sep 17, 9:09 pm, "William Stein" <[EMAIL PROTECTED]> wrote:
> On Wed, Sep 17, 2008 at 8:59 PM, John H Palmieri <[EMAIL PROTECTED]> wrote:
>
> > sage: is_FractionField(FractionField(ZZ))
> > False
>
> > Oy. This seems to be intentional: there is a doctest very similar to
> > this. It doesn't seem right, though. How hard would it be to change?
> > Is it worth it?
>
> In most cases in Sage (maybe all cases), is_Foo is a data type
> check. It's not making a mathematical assertion. The implementation
> is almost always a call to isinstance.
Right, I saw that in the source code. How about we change it, in this
case, from
return isinstance(x, FractionField_generic)
to
return isinstance(x, (FractionField_generic, Field))
(Every field is its own fraction field.) I can submit a trac ticket
with this change, unless someone convinces me that it's a really bad
idea.
>
> > Along the same lines, partial fraction decomposition should work for
> > rational numbers; this would work if elements of QQ were instances of
> > FractionFieldElement, right?
>
> Or you could just implement it, which would likely be a good idea.
It might be a good idea, but I don't know how to do it. How do I
produce, given 1/20, the output 1/4 - 1/5? That is, how do I tell
sage to output 1/4 - 1/5, as an element in QQ, I suppose, without
evaluating it and just printing 1/20?
>
> William
>
John
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