This is ticket #29469 <https://trac.sagemath.org/ticket/29469>, now!
On Monday, March 30, 2020 at 8:41:40 AM UTC+2, Sebastian Oehms wrote: > > in the former case it raises a NotImplementedError even if inversion is > possible: > > sage: P.<x,y> = QQ[] > sage: Q = P.quo([1-x*y]) > sage: Q.inject_variables() > Defining xbar, ybar > sage: ybar.is_unit() > Traceback (most recent call last): > ... > NotImplementedError: > > but: > > sage: ~ybar > xbar > > This is marked as a TODO in the docstring: > > Return True if self is a unit in the quotient ring. > > TODO: This is not fully implemented, as illustrated in the example > below. So far, self is determined to be unit only if its > representation in the cover ring R is also a unit. > > In the latter case the NotImplementedError is raised even if the preimage > in the cover is a unit. > > sage: Z16x.<x> = Integers(16)[] > sage: S.<y> = Z16x.quotient(x^2 + x + 1) > sage: S(3).is_unit() > Traceback (most recent call last): > ... > NotImplementedError: The base ring (=Ring of integers modulo 16) is not a > field > > > Here accordingly, inversion is not possible in such cases. > > If there is no special reason why this hasn't been done, I will open a > ticket to fill that in! > > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/1b6e24ee-9679-409d-b523-3d6259279fd5%40googlegroups.com.
