#12123: Bug in convolution in old Piecewise
-----------------------------+------------------------
Reporter: kcrisman | Owner: burcin
Type: defect | Status: new
Priority: minor | Milestone: sage-7.3
Component: calculus | Resolution:
Keywords: piecewise | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps: todo
-----------------------------+------------------------
Changes (by mkoeppe):
* cc: kcrisman, jondo, vbraun, slelievre, mkoeppe, eviatarbach, rws
(added)
* priority: major => minor
* milestone: sage-6.4 => sage-7.3
* keywords: => piecewise
Old description:
> {{{
>
> sage: x = PolynomialRing(QQ,'x').gen()
> sage: f = Piecewise([[(-2, 2), 2 * x^0]])
> sage: g = Piecewise([[(0, 2), 3/4 * x^0]])
> sage: n = f.convolution(g)
>
> sage: n
> Piecewise defined function with 3 parts, [[(-2, 0), 3/2*x + 3], [(0, 2),
> 6], [(2, 4), -3/2*x + 6]]
> }}}
> But the middle piece should be 3, not 6, apparently.
>
> See the original report at [http://ask.sagemath.org/question/965
> /convolution-got-the-wrong-result this ask.sagemath.org question].
New description:
The old Piecewise (pre #14801; now deprecated) has this bug:
{{{
sage: x = PolynomialRing(QQ,'x').gen()
sage: f = Piecewise([[(-2, 2), 2 * x^0]])
sage: g = Piecewise([[(0, 2), 3/4 * x^0]])
sage: n = f.convolution(g)
sage: n
Piecewise defined function with 3 parts, [[(-2, 0), 3/2*x + 3], [(0, 2),
6], [(2, 4), -3/2*x + 6]]
}}}
But the middle piece should be 3, not 6, apparently.
See the original report at [http://ask.sagemath.org/question/965
/convolution-got-the-wrong-result this ask.sagemath.org question].
Note this is fixed in the new `piecewise` (lowercase p, from #14801).
{{{
sage: x = PolynomialRing(QQ,'x').gen()
sage: f = piecewise([[(-2, 2), 2 * x^0]])
sage: g = piecewise([[(0, 2), 3/4 * x^0]])
sage: n = f.convolution(g)
sage: n
piecewise(x|-->3/2*x + 3 on (-2, 0], x|-->3 on (0, 2], x|-->-3/2*x + 6 on
(2, 4]; x)
}}}
Can close this bug when the old `Piecewise` is removed completely.
--
Comment:
Description modified to comment that this seems fixed in the new
`piecewise` (#14801).
--
Ticket URL: <https://trac.sagemath.org/ticket/12123#comment:12>
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