Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3364 by [email protected]: RealInterval.refine() changes the
order of the endpoints
http://code.google.com/p/sympy/issues/detail?id=3364
Minimal example:
from sympy import var, legendre_poly
from sympy.polys.rootisolation import RealInterval
from sympy.polys import ZZ
from sympy.polys.domains.pythonrationaltype import PythonRationalType
var("x")
p = legendre_poly(4, x)
a = PythonRationalType(-1, 1)
b = PythonRationalType(-1, 2)
r = RealInterval((a, b), p.as_poly().rep.rep, ZZ)
print r.a, r.b, r.a < r.b, r.dx
r = r.refine()
print r.a, r.b, r.a < r.b, r.dx
This prints:
-1/1 -1/2 True 1/2
-2/3 -1/1 False -1/3
As you can see, first the interval is fine and a < b as it should be. Then
we call refine and suddenly it's not true that a < b, and also the dx < 0.
I think that this is a bug.
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