ncpolopt

Sparse SDP relaxations of polynomial optimization problems with noncommuting variables — the NPA hierarchy and its relatives. ncpolopt is a modern rewrite of the GPL-3 ncpol2sdpa package: the same hierarchies and the same four solver backends, behind a fresh, typed API built on dataclasses and lazy solver discovery.

• NPA hierarchy for noncommutative operators, plus the Moroder (PPT), steering, and RDM (reduced density matrix) hierarchies.
• Lasserre-style hierarchies for commuting variables, with an optional chordal sparsity extension (SparsePOP-style) that splits the relaxation into independent moment blocks per clique.
• Four solver backends: cvxpy, MOSEK, PICOS/cvxopt, and the external SDPA binary — selected by name or auto-detected.
• Moment expressions (MomentEntry) instead of a string DSL for writing conditions on the moment matrix directly.

Installation

Requires Python 3.13+. The core package needs only numpy, scipy, and sympy; install a solver extra to actually solve:

uv pip install ncpolopt[cvxpy]        # or: pip install ncpolopt[cvxpy]

Available extras: cvxpy, mosek, cvxopt (PICOS + cvxopt), chordal (chompack, only needed for the chompack completion method), and all. With no solver installed the package still imports and builds relaxations; only solving raises a SolverError telling you which extra to install.

Quickstart

A tiny noncommutative problem: two Hermitian operators x0, x1, minimize the anticommutator x0*x1 + x1*x0 under the constraint x1 - x1² + ½ ≥ 0 and the projection x0² = x0:

import ncpolopt as nc

X = nc.generate_operators("x", 2, hermitian=True)
problem = nc.Problem(
    X,
    objective=X[0] * X[1] + X[1] * X[0],
    inequalities=[-X[1] ** 2 + X[1] + 0.5],
    substitutions={X[0] ** 2: X[0]},
)
solution = problem.solve(level=2)
print(solution.primal)   # -0.75

Object model

Work flows through three layers, each a frozen dataclass:

1. Problem — the symbolic model: variables (a list of lists for multipartite problems), objective, polynomial and moment constraints, substitution rules. Reusable; building a relaxation never mutates it.
2. NpaRelaxation — the SDP at a hierarchy level, built by problem.relaxation(level) or subclass hierarchies MoroderHierarchy, SteeringHierarchy, RdmHierarchy. The assembled SDP data (relaxation.sdp) is a frozen blockwise COO representation.
3. Solution — the immutable solve result (primal, dual, status, x_mat, y_mat) with extraction helpers: monomial_value(), dual_value(), dual_block(), sos_decomposition(), solution_ranks().

Command line

ncpolopt                # version, platform, detected solvers
ncpolopt --version

Development

uv sync --group dev
uv run pytest
uv run ruff check .

License

GPL-3.0-only. This package is derived from ncpol2sdpa, which is Copyright (C) 2012-2016 Peter Wittek and contributors.