LinearFunctionOrConstraint.__richcmp__ should replace before converting

[jdemeyer]

The logic in the hack to allow linear functions like x_0 <= x_1 <= x_2 is wrong: currently, when doing x <= y, it first converts x and y to the correct parent and then it checks for a chained comparison. This is wrong: it should check for a chained comparison on the input of the __richcmp__ function before converting.

One consequence is that the following does not work as expected:

sage: p.<x> = MixedIntegerLinearProgram()
sage: from sage.numerical.linear_functions import LinearFunctionsParent
sage: LF = LinearFunctionsParent(QQ)
sage: 3 <= x[0] <= LF(4)
x_0 <= 4

CC: @vbraun

Component: linear programming

Author: Jeroen Demeyer

Branch/Commit: 4606309

Reviewer: Marc Mezzarobba

Issue created by migration from https://trac.sagemath.org/ticket/24423

[jdemeyer]

Branch: u/jdemeyer/linearfunctionorconstraint___richcmp___should_replace_before_converting

[jdemeyer]

Commit: aba680c

[jdemeyer]

New commits:

aba680c

LinearFunctionOrConstraint.__richcmp__ should replace before converting

[sagetrac-git]

Changed commit from aba680c to 4606309

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

4606309

LinearFunctionOrConstraint.__richcmp__ should replace before converting

[mezzarobba]

comment:6

Can't really say I understand all implications, but this looks at least as reasonable as the previous version :-).

[mezzarobba]

Reviewer: Marc Mezzarobba

[jdemeyer]

comment:7

Thanks!

[vbraun]

Changed branch from u/jdemeyer/linearfunctionorconstraint___richcmp___should_replace_before_converting to 4606309