Yes, I'm working on the coercion now. However, isn't a==0 checking coercion from the parent of a to the parent of 0. In other words, the homset of rational points on P and QQ.
In dimension 1, there is a canonical coercion, but not in higher dimensions. On Thursday, September 7, 2017 at 12:17:57 PM UTC-5, David Roe wrote: > > The reason that a==0 returns false is that there is no coercion map from > QQ to P: > > sage: P.has_coerce_map_from(QQ) > False > > I'm not convinced that there should be a coercion, it's pretty rare that a > scheme has a natural map from its base ring. > However, it seems like there's also a problem hiding here, probably > because schemes don't use the coercion model properly: > > sage: P.convert_map_from(QQ) > Traceback (most recent call last) > ... > RuntimeError: BUG in coercion model, no element constructor for <class > 'sage.schemes.projective.projective_space.ProjectiveSpace_rational_field_with_category'> > > David > > On Thu, Sep 7, 2017 at 1:11 PM, Ben Hutz <bn4...@gmail.com <javascript:>> > wrote: > >> I'm working on implementing coercion for scheme points and had a question >> about how comparison is done. As an explicit example consider the following >> point >> >> P.<u,v>= ProjectiveSpace (QQ ,1) >> a=P(0) >> >> in particular, the integer 0 is coerced into the projective point (0:1). >> For comparisons it appears that >> >> a == P(0) (returns to True) >> >> calls the _richcmp_() function so uses the coercion framework, but >> >> a==0 (returns False even though it knows there is a coercion from the >> integer ring to P) >> >> is calling something else. There does not appear to be an __eq__() >> operator implemented for scheme points, but it does show up in tab >> completion in the notebook, but can't tell me where the code is from. Is >> this an artifact of starting to transition the code to python3. Or this >> just broken somewhere? >> >> Thanks, >> Ben >> >> -- >> 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+...@googlegroups.com <javascript:>. >> To post to this group, send email to sage-...@googlegroups.com >> <javascript:>. >> Visit this group at https://groups.google.com/group/sage-devel. >> For more options, visit https://groups.google.com/d/optout. >> > > -- 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 post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
