#17700: wrong symbolic results in case the answer is not known
--------------------------------+------------------------
Reporter: jakobkroeker | Owner:
Type: defect | Status: new
Priority: critical | Milestone: sage-6.7
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps: todo
--------------------------------+------------------------
Comment (by rws):
The ticket is about symbolics so let's get concrete. It happens that at
the moment I'm implementing more logic affecting
comparisons/relations/zero tests of expressions in Pynac. The decision
process for the logic in Sage is:
`Expression.__nonzero__()` is called on input of `bool` but also (!)
indirectly from Pynac for any call of `numeric::is_zero()` which is a lot
of times. `__nonzero__` is the one that should throw an exception for
unknown results. In `__nonzero__`,
1. first the relations of constants are decided
1. Pynac's `relational_to_bool` is called (`relational::safe_bool()`), it
does:
1. relations with one or two infinities; any result gets returned by
`__nonzero__` right away
1. if l.h.s - r.h.s is a Python object (other than `Expression`)
compare it to zero, i.e., delegate to the resp. class
1. the previous result may now get changed in case of not-equal; already
here Maxima may be called (I think this is wrong, Maxima should always be
the last resort)
1. if no assumptions are needed now is time for `test_relation` which has
some detailed logic and uses interval fields to disprove relations
("interval fields never return false positives"); it already has tristate
logic by returning `NotImplemented` if unsure
1. if the previous neither returns `True/False` return what
`symbolic/relation.py:test_relation_maxima()` returns
1. the relation is tested and any `True` is returned immediately
1. simplification is attempted before returning the final `True/False`
--
Ticket URL: <http://trac.sagemath.org/ticket/17700#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/d/optout.
