On Thu, Sep 7, 2017 at 2:00 PM, Ben Hutz <bn4...@gmail.com> wrote: > 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. >
Once you construct P(0), both a and P(0) are in the same parent, so there are no coercions involved in the test a==P(0). In your branch, what does sage: a.parent().coerce_map_from(QQ) return? > 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. > I certainly agree that leaving off the last coordinate is convenient and common. But the difference is between *conversion* (where you specify the parent explicitly) and *coercion* (which happens implicitly, like in the equality test you're making above). Are you trying to add coercions, just for A^1 and P^1? Or something more? David > 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> 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. >>> 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+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. > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. 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