wrong piecewise convolution

[rwst]

This doctest tests against a wrong result, the resulting curve must have a quadratic part:

            sage: f = piecewise([[(-1,1),1]])                             ## example 2
            sage: g = piecewise([[(0,3),x]])
            sage: f.convolution(g)
            Piecewise defined function with 3 parts, [[(-1, 1), 0], [(1, 2), -3/2*x], [(2, 4), -3/2*x]]

From numerical investigation it seems the solution would be piecewise(x|-->1/2*x^2 + x + 1/2 on (-1/2, 1), x|-->2*x on (1, 2), x|-->-1/2*x^2 + x + 4 on (2, 7/2); x).

This works in the new piecewise from #14801.

The ticket is for documentary reasons because a new piecewise code is being worked on in #14801.

CC: @wdjoyner @kcrisman @jondo @vbraun @slel @mkoeppe @eviatarbach @rwst

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/17793

[kcrisman]

comment:1

See also #12123 (possibly the same?) Actually, the fix should be pretty easy once one understands the code, but I gave up here.

[mkoeppe]

comment:3

Works in the new piecewise from #14801.
Dup of #12123, which is why I'm setting this to "dup/needs review"

[embray]

comment:6

Determined to be invalid/duplicate/wontfix (closing as "wontfix" as a catch-all resolution).