Solvers

This package contains all solver implementations and required utility scripts.

Installation

pip install muoblpsolvers

Or use any other package manager.

Alternatively you can install locally (see Development).

C++ python bindings

C++ bindings live in the monorepo subproject bindings/ (muoblpbindings).

Solvers

PuLP name / class module / experiments solver_type / bindings-backed / constructor options:

Modules are under src/muoblpsolvers/.

Solver contract

All solvers follow PuLP's LpSolver contract:

• Constructor: Solver(msg=True, timeLimit=None, options=None, **solver_options); solver options are keyword arguments, stored in optionsDict and serialized by toDict()/toJson() (None kwargs are dropped by PuLP).
• available(): True for pure-python solvers; bindings-backed solvers return whether muoblpbindings imports (imports are lazy, so import muoblpsolvers works without bindings).
• Status: actualSolve(lp) sets lp.status and returns it.
• msg=False: no output during solve.
• timeLimit: Greedy, Phragmen, MES-Exponential and MES-Constrains (coarsely, per iteration) stop early with LpStatusNotSolved; SummedObjectives passes it to CBC/Gurobi; other bindings-backed solvers emit a warning and ignore it.
• Validation: all PB solvers (all except SummedObjectives) reject programs outside the binary PB shape — no objectives, non 0/1 variables, negative utilities or costs — with PulpSolverError.
• Known limitation: MES-family, STV, ExpandingApprovals and SolidCoalitionRefinement ignore lower-bound (>=) constraints.

Example Solver

1. See example SummedObjectivesLpSolver
2. Solver has to be a class that extends LpSolver
3. Solver needs to override method actualSolve to accept an instance of MultiObjectiveLpProblem, set lp.status and return it

PuLP registration

import muoblpsolvers registers all 10 solvers into PuLP's registry, so they resolve through the standard PuLP API:

import muoblpsolvers  # side effect: registers solvers
import pulp

solver = pulp.getSolver("Phragmen", kappa=2.0)  # any of the 10 names
"Phragmen" in pulp.listSolvers()                 # True

Registered names: ExpandingApprovals, Greedy, MethodOfEqualSharesAdd1, MethodOfEqualSharesConstrains, MethodOfEqualSharesExponential, MethodOfEqualSharesUtility, Phragmen, SingleTransferableVote, SolidCoalitionRefinement, SummedObjectives.

Mechanism. PuLP 3.3.2 drives getSolver/listSolvers off the module-level list pulp.apis._all_solvers (getSolver builds {cls.name: cls} from it). Registration appends our solver classes to that list in place. It runs automatically on import via register_solvers() (also exported for explicit use); the function is idempotent and only appends classes, so it never instantiates a solver and stays bindings-free (C++ binding imports are lazy, inside each solver's actualSolve).

Development

core and bindings are path dependencies; poetry install compiles bindings from ../bindings (C++20 toolchain, see bindings README).

$ cd multiobjective-lp/solvers # package root
$ poetry install
$ poetry run pytest
$ poetry run pyright
$ poetry run ruff check .. && poetry run ruff format --diff ..  # CI ruff version