#20461: Fixes for copying a MIP and its variables
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Reporter: mkoeppe | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: numerical | Keywords: lp
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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Even after merging #20414, both `copy` and (the identical) `deepcopy` have
weird semantics in relation to the `MIPVariable`s in a problems -- because
a MIP does not have an API to gain access to its variables; and trying to
use the old `MIPVariable`s with the copy is questionable and definitely
broken if one creates new components of this variable, see #15159, #19523.
Same when there's no explicit `MIPVariable` and only the
`_default_mipvariable` is used via the problem's `__getitem__` method.
Here's a possible fix without having to change the whole design:
* a new `MixedIntegerLinearProgram.copy` method that takes a `names`
keyword argument, enabling this operation:
{{{
sage: p.<x,y> = MixedIntegerLinearProgram()
sage: q.<newx,newy> = p.copy()
}}}
* `copy` and `__copy__` (and `__deepcopy__`) should make a copy of
_default_variable (this requires writing a `__copy__` method for
`MIPVariable`)
* if `MixedIntegerLinearProgram.new_variable` has been called, it should
set a flag and then if __copy__ (or __deepcopy__) are called, it should
display a warning (deprecation??) and refer the user to the new `copy`
method.
--
Ticket URL: <http://trac.sagemath.org/ticket/20461>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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