Yes, but *after* implementing the coercion for the homsets I'm getting the behavior above. The 'a==0' doesn't go through the coecion framework, but the a==P(0) does. So one returns true and the other false. I'm trying to figure out why == is not utilizing the coercion/richcmp in that case.
You'd be surprised at how often in Sage the shorthand of leaving of the last coordinate occurs. But, yes, it is just a shorthand and is used in the __init__() for point. On Thursday, September 7, 2017 at 12:53:05 PM UTC-5, David Roe wrote: > > > > On Thu, Sep 7, 2017 at 1:46 PM, Ben Hutz <bn4...@gmail.com <javascript:>> > wrote: > >> 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. >> > > Yes, I got confused by the notation, since normally in Sage P(0) would > create an element of P. But there's still no coercion: > > sage: a.parent().has_coerce_map_from(QQ) > False > > In dimension 1, there is a canonical coercion, but not in higher >> dimensions. >> > > Sure, but only for P^1 and A^1, not other curves. Is there value in > having coercions just for those two, for dynamics for example? > David > > 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> 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. >>>> To post to this group, send email to sage-...@googlegroups.com. >>>> 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+...@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.
