#7712: error with polynomial with interval coefficients
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Reporter: zimmerma | Owner: AlexGhitza
Type: defect | Status: new
Priority: major | Milestone: sage-5.6
Component: basic arithmetic | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Description changed by zimmerma:
Old description:
> 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
> }}}
New description:
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#comment:14>
Sage <http://www.sagemath.org>
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