#20461: Fixes for copying a MIP and its variables
-----------------------------------+------------------------
Reporter: mkoeppe | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.3
Component: numerical | Resolution:
Keywords: lp | Merged in:
Authors: Matthias Koeppe | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
-----------------------------------+------------------------
Changes (by {'newvalue': u'Matthias Koeppe', 'oldvalue': ''}):
* milestone: sage-7.2 => sage-7.3
* author: => Matthias Koeppe
Old description:
> 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:
>
> {{{
> sage: sage: p = MixedIntegerLinearProgram()
> sage: p[0]
> x_0
> sage: q = copy(p)
> sage: q[0]
> x_0
> sage: q[1]
> x_1
> sage: sage: p.number_of_variables()
> 2
> sage: sage: q.number_of_variables()
> 1
> }}}
>
> 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()
> }}}
> and the less magical syntax
> {{{
> sage: q, newx, newy = p.copy([x, y])
> }}}
> * `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.
New description:
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:
{{{
sage: sage: p = MixedIntegerLinearProgram()
sage: p[0]
x_0
sage: q = copy(p)
sage: q[0]
x_0
sage: q[1]
x_1
sage: sage: p.number_of_variables()
2
sage: sage: q.number_of_variables()
1
}}}
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()
}}}
and the less magical syntax
{{{
sage: q, newx, newy = p.copy([x, y])
}}}
* `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.
In this ticket, we take care of the default MIP variable.
#20657 will take care of the variables created with `new_variable`.
--
--
Ticket URL: <http://trac.sagemath.org/ticket/20461#comment:8>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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