#20302: Clean up MILP backend interface
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Reporter: mkoeppe | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: numerical | Resolution:
Keywords: lp | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Old description:
> While implementing `InteractiveLPBackend` for #20296, I noticed several
> deficiencies in the design of the MILP backend interface.
>
> - `add_col` and `add_variable` both add a variable to the problem; but
> `add_col` only allows to add a column with no name; whereas
> `add_variable` only allows to add a column with no coefficients. There
> should be one function (`add_variable`, probably - see #20296 for a
> possible interface) that can do both; should then deprecate `add_col`.
> (Also compare with `add_linear_constraint`, which takes a zipped
> index/coefficient list, whereas `add_col` takes two parallel lists.)
>
> - `variable_upper_bound`: This interface is bizarre. Can't remove an
> upper bound from a variable because `None` means both 'no upper bound'
> and 'get the upper bound'. Likewise `variable_lower_bound`. (Moreover,
> there's redundancy with `col_bounds`.)
>
> - `add_variables` and `add_linear_constraints` should have a default
> implementation in `GenericBackend`, like `add_linear_constraint_vector`.
>
> Also, I think the backends should be tested using a common `TestSuite`.
> Right now each backend uses its own doctests, which have slightly
> diverged from each other, so there is nothing (other than the fact that
> they were the result of copy-paste from each other) that ensures
> consistency. (#20296 fixes several wrong doctests in `GenericBackend`,
> from which I tried to copy-paste, for example.)
New description:
While implementing `InteractiveLPBackend` for #20296, I noticed several
deficiencies in the design of the MILP backend interface.
- `add_col` and `add_variable` both add a variable to the problem; but
`add_col` only allows to add a column with no name; whereas `add_variable`
only allows to add a column with no coefficients. There should be one
function (`add_variable`, probably - see #20296 for a possible interface)
that can do both; should then deprecate `add_col`. (Also compare with
`add_linear_constraint`, which takes a zipped index/coefficient list,
whereas `add_col` takes two parallel lists.)
- `add_variables` and `add_linear_constraints` should have a default
implementation in `GenericBackend`, like `add_linear_constraint_vector`.
Also, I think the backends should be tested using a common `TestSuite`.
Right now each backend uses its own doctests, which have slightly diverged
from each other, so there is nothing (other than the fact that they were
the result of copy-paste from each other) that ensures consistency.
(#20296 fixes several wrong doctests in `GenericBackend`, from which I
tried to copy-paste, for example.)
--
Comment (by mkoeppe):
Description modified to remove my comments about `variable_upper_bound`
and `variable_lower_bound`. I was misled by the interface description in
`generic_backend`, which was out of sync with the real backends. Fixed in
#20296.
--
Ticket URL: <http://trac.sagemath.org/ticket/20302#comment:2>
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