#15815: rational preimages for projective morphisms returns incorrect points
-------------------------------------+-------------------------------------
Reporter: bhutz | Owner: bhutz
Type: defect | Status: needs_review
Priority: minor | Milestone: sage-6.2
Component: algebraic | Resolution:
geometry | Merged in:
Keywords: | Reviewers:
Authors: Ben Hutz | Work issues:
Report Upstream: N/A | Commit:
Branch: | e43132a4054660d545733cbb2ab17dd56afbaf81
u/bhutz/ticket/15815 | Stopgaps:
Dependencies: |
-------------------------------------+-------------------------------------
Changes (by bhutz):
* status: needs_info => needs_review
Comment:
Here is a longer description. The goal is to find all rational solutions
to a zero dimensional ideal in projective space. The method is just basic
elimination theory: compute an elimination ideal and solve one variable at
a time. As each variable is solved the values are stored in {{{points}}}.
The initial test was to check if there was an actual rational solution,
i.e. we had a rational value for each of the N+1 variables. So to answer
one question, the test would pass when there was a rational value for all
N+1 variables.
The issue is that for higher dimensions there may be multiple equations
involving one of the variables, one of which does and one of which does
not have a rational solution. These slipped through to give wrong values.
The test was modified to check that the "solution" really was a zero for
*all* defining equations of the ideal.
As for the content of the branch matching the description. This seems
clear to me. This is a modification to the {{rational_preimages}}}
function to correct the particular problem I just described in more detail
by adding the test I described. However, I did neglect to update it to say
that I also added a simple codomain check to ensure that the base point
was in the codomain of the function. Is that the point of confusion
between description and branch?
If this is still not clear to you with this more verbose description, then
I need a more specific question.
--
Ticket URL: <http://trac.sagemath.org/ticket/15815#comment:7>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
