I think you've uncovered a bug that had been masked by the is_one bug.
If I'm not mistaken, I^-1 calls MultiplicativeGroupElement.__invert__,
which tests whether self is one and if not returns 1/self. Obligingly,
the coercion model (being asked to calculate 1/self) calls __invert__
again!
(I convinced myself of this by making is_one print a warning every
time it is called. Then running your example code prints the warning
over and over again, until the maximum recursion depth is exceeded and
a segfault is raised.)
David
On Dec 5, 4:48 pm, "John Cremona" <[EMAIL PROTECTED]> wrote:
> How worrying is this:
>
> In 3.2.1 we have:
> {{{
> sage: K.<a>=QuadraticField(2310)
> sage: C=K.class_group()
> sage: I=C.0
> sage: I^-1
> AttributeError
> ...
> AttributeError: 'FractionalIdealClass' object has no attribute 'is_one'}}}
>
> (cf #1052).
>
> Now I add one line in sage/rings/number_field/class_group.py, namely I add
> is_one = is_principal
> inside the code for class FractionalIdealClass.
>
> Result:
> {{{
> sage: K.<a>=QuadraticField(2310)
> sage: C=K.class_group()
> sage: I=C.0
> sage: I^-1
> /local/jec/sage-3.2.1.rc1/local/bin/sage-sage: line 202: 15960
> Segmentation fault sage-ipython "$@" -p sage -i
>
> }}}
>
> I did not think that adding one line pf python code could do that....
>
> John
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