oximo-highs

HiGHS LP/MILP backend for oximo.

Wraps the highs crate (HiGHS bundled, no separate install required). Supports LP, MILP, and convex continuous QP model kinds.

Usage

Most users should depend on the umbrella oximo crate with the highs feature (enabled by default):

[dependencies]

oximo = "0.1"

To use this crate directly:

[dependencies]

oximo-highs = "0.1"

oximo-core   = "0.1"

oximo-solver = "0.1"

Quick example

use oximo_core::prelude::*;
use oximo_highs::{Highs, HighsOptions};
use oximo_solver::{Solver, SolverStatus};

let m = Model::new("toy");
let x = m.var("x").lb(0.0).build();
let y = m.var("y").lb(0.0).ub(4.0).build();
m.constraint("c1", (x + 2.0 * y).le(14.0));
m.constraint("c2", (3.0 * x - y).ge(0.0));
m.maximize(3.0 * x + 4.0 * y);

let result = Highs.solve(&m, &HighsOptions::default()).unwrap();
assert_eq!(result.status, SolverStatus::Optimal);
println!("obj = {}", result.objective.unwrap()); // 34.0
println!("x   = {}", result.value_of(x).unwrap()); // 6.0
println!("y   = {}", result.value_of(y).unwrap()); // 4.0

Quadratic programs (QP)

A quadratic objective (e.g. x.powi(2), x * y) with linear constraints is detected as QP and solved by uploading the Hessian Q via Highs_passHessian. oximo derives Q from the objective with oximo_expr::extract_quadratic; HiGHS then minimizes c'x + 0.5·x'Qx.

use oximo_core::prelude::*;
use oximo_highs::{Highs, HighsOptions};
use oximo_solver::{Solver, SolverStatus};

let m = Model::new("qp");
let x = m.var("x").lb(-10.0).ub(10.0).build();
let y = m.var("y").lb(-10.0).ub(10.0).build();
m.constraint("c", (x + y).eq(1.0));
m.minimize(x.powi(2) + y.powi(2)); // min x^2 + y^2

let result = Highs.solve(&m, &HighsOptions::default()).unwrap();
assert_eq!(result.status, SolverStatus::Optimal); // x = y = 0.5, obj = 0.5

Convexity. HiGHS supports only convex QPs. For minimization, Q must be positive semidefinite (PSD), and for maximization, Q must be negative semidefinite (NSD). HiGHS does not check this condition, so supplying an indefinite or incorrectly signed Hessian may lead to incorrect or non-optimal solutions.

HiGHS does not support MIQP (integer + quadratic, returned as UnsupportedKind) or quadratic constraints (returned as Nonlinear).

Options

HighsOptions is a typed builder. All methods return Self for chaining.

HighsMethod variants: Choose (let HiGHS decide), Simplex, Ipm (interior-point), PdLp (first-order).

HighsPresolve variants: Off, On, Auto ("choose").

use std::time::Duration;
use oximo_highs::{HighsOptions, HighsMethod, HighsPresolve};
use oximo_solver::UniversalOptionsExt;

let opts = HighsOptions::default()
    .time_limit(Duration::from_secs(60))
    .threads(4)
    .mip_gap(0.01)
    .presolve(HighsPresolve::On)
    .method(HighsMethod::Ipm)
    .parallel(true);

Result

SolverResult fields populated on Optimal or Feasible:

• objective - objective value (adjusted for any constant term)
• primal - variable values, keyed by VarId; access via result.value_of(var)
• dual - constraint duals, keyed by ConstraintId
• reduced_costs - variable reduced costs, keyed by VarId
• solve_time - wall time measured around the HiGHS solve call

License

MIT OR Apache-2.0