Hi Thomas,
sorry, I first got your mail off-list, and thought that you did not post
here.
On 2013-07-05, Thomas Feulner <thomas.feul...@uni-bayreuth.de> wrote:
> You are right, maybe my example was to tiny. Here is another one, which
> also initializes the
> QuotientRing_nc, too:
>
> sage: from sage.rings.quotient_ring import QuotientRing_nc
> sage: class Y(Parent):
> ....: def __init__(self, gens, names):
> ....: Parent.__init__(self, Integers(), gens=gens, names=
> names)
> sage: class X(Y, QuotientRing_nc):
> ....: def __init__(self, R, I):
> ....: Y.__init__(self, gens=[R.gen(0), R.gen(1)], names=['x'
> , 'y'])
> ....: QuotientRing_nc.__init__(R, I)
> sage: R = PolynomialRing(Integers(), 'a,b,c')
> sage: R.ideal(R.gen(0))
> Ideal (a) of Multivariate Polynomial Ring in a, b, c over Integer Ring
> sage: x = X(R, I)
>
> But the problem is still there. Do you have any other suggestions?
QuotientRing_nc inherits a placeholder method ngens from ParentWithGens.
This needs to be implemented. In the code below, I hardcode that the
number of generators is two, but of course in real applications one
needs to do something more fancy.
In any case, when QuotientRing_nc.__init__(self,...) is called, then
self.ngens() must be able to return the correct answer.
Moreover, it seems to be needed to first call QuotientRing_nc.__init__
and call Y.__init__ only after that. It is not totally clear to me why
this is needed. Anyway, the following does not crash:
sage: class Y(Parent):
....: def __init__(self, gens, names):
....: V = Integers()**2
....: Parent.__init__(self, Integers(), gens=(V.gen(0), V.gen(1)),
names=names)
....:
sage: R.<a,b,c> = ZZ[]
sage: I = R*[a]
sage: class X(Y, QuotientRing_nc):
....: def __init__(self, R, I):
....: QuotientRing_nc.__init__(self, R, I, names=['x', 'y'])
....: Y.__init__(self, gens=[R.gen(0), R.gen(1)],
names=self.variable_names())
....: def ngens(self):
....: return 2
....:
sage: x = X(R, I)
sage: x
Quotient of Multivariate Polynomial Ring in a, b, c over Integer Ring by the
ideal (a)
sage: x.variable_names()
('x', 'y')
Note that I use names=self.variable_names() in Y.__init__ just for fun.
When it is called, the variable_names() are already available.
Best regards,
Simon
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