#7712: error in polynomial substitution with interval coefficients
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Reporter: zimmerma | Owner: AlexGhitza
Type: defect | Status: new
Priority: major | Milestone: sage-4.3
Component: basic arithmetic | Keywords:
Work_issues: | Author:
Upstream: N/A | Reviewer:
Merged: |
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Consider the following example:
{{{
sage: P.<y,z> = PolynomialRing(RealIntervalField(2))
sage: Q.<x> = PolynomialRing(P)
sage: C = (y-x)^3
sage: C(y/2)
0
}}}
I do not understand why the result is 0. In fact there are two
errors:
(i) the result is a polynomial of degree 3 in y, thus y**3 should appear
(ii) the result should "contain" the exact result which is 0.125*y**3,
thus it should be c*y**3 where c is an interval containing
0.125. Compare the following with a precision of 10 bits:
{{{
sage: P.<y,z> = PolynomialRing(RealIntervalField(10))
sage: Q.<x> = PolynomialRing(P)
sage: C = (y-x)^3
sage: C(y/2)
0.12500?*y^3
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7712>
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