spin-sim

Pure-Rust Ising and XY Monte Carlo on periodic lattices: hypercubic, or any Bravais lattice given by forward neighbor offsets (Lattice::with_offsets).

Algorithms

Single-spin flips (Metropolis, Gibbs)
Swendsen-Wang cluster updates
Wolff single-cluster updates
Parallel tempering (replica exchange)
Overlap cluster moves (Houdayer / pairN / Jörg / CMR / permN / gpermN / replica Monte Carlo) for spin glasses
Open and antiperiodic boundaries as a coupling transform (Lattice::boundary_factors)

Replicas are parallelized over threads with rayon.

Usage

use spin_sim::config::*;
use spin_sim::{Lattice, Realization, run_sweep_loop};

let lattice = Lattice::new(vec![16, 16]);
let temps = vec![2.0, 2.27, 2.5];
let n_replicas = 2;

// A fixed ±1 pattern (+1 along axis 0, -1 along axis 1) is unfrustrated;
// draw random signs per bond for a ±J spin glass.
let couplings: Vec<f32> = (0..lattice.n_spins * lattice.n_neighbors)
    .map(|i| if i % 2 == 0 { 1.0 } else { -1.0 })
    .collect();

let mut real = Realization::new(&lattice, couplings, &temps, n_replicas, 42);

let config = SimConfig {
    n_sweeps: 10_000,
    warmup_sweeps: 1_000,
    sweep_mode: SweepMode::Metropolis,
    cluster_update: None,
    pt_interval: Some(1),
    pt_schedule: PtSchedule::FullLadder,
    overlap_cluster: None,
    autocorrelation_max_lag: None,
    autocorrelation_backend: AutocorrelationBackend::Ring,
    sequential: false,
    equilibration_diagnostic: false,
    conditional_link_overlap: true,
};

use std::sync::atomic::AtomicBool;
let interrupted = AtomicBool::new(false);
let result = run_sweep_loop(
    &lattice, &mut real, n_replicas, temps.len(), &config, &interrupted, &|| {}, 0,
).unwrap();

println!("energies: {:?}", result.energies);

Upgrading from 0.2.0

0.3.0 changes public struct literals and enums; no legacy wrapper types are provided. To keep 0.2.0's move schedule:

ClusterConfig and OverlapClusterConfig: add action: ClusterAction::Update (cluster graphs can now also be observed without flipping spins).
OverlapClusterConfig: add max_temperature: None.
SimConfig: add pt_schedule: PtSchedule::SingleRandomEdge and autocorrelation_backend: AutocorrelationBackend::Ring.
OverlapClusterBuildMode::Jorg is now Jorg(usize); use Jorg(2). The new variants Pair(usize) and Rmc, and SweepMode::None, break exhaustive matches.

Realization seeds are now derived per system rather than base_seed + i, so a given seed produces different trajectories than in 0.2.0.

Also new in 0.3.0:

SimConfig::validate is an inherent method returning Result<(), String>; the validator dependency is gone. SimConfig has a new field conditional_link_overlap (set true to keep the link-overlap sums per overlap bin) and XyConfig a new field measure_interval (set 1).
Overlap modes Perm(usize) and GaugedPerm(usize) break exhaustive matches; their size must be between 2 and 8, as validation now enforces.
Moments of a call that measured nothing are NaN instead of zero, and a τ of a series without variance is NaN instead of 0.5. Each τ has a *_converged flag.
Interval events keep their phase across calls; reset restarts it.
Lattices with an extent of 1 are rejected.
SweepResult, ClusterStats, Diagnostics and GraphObservationSummary gained fields (per-disorder samples, energy τ, FK visit counts, overlap and replica Monte Carlo counters, 3D wrapping and cluster moments).
Swendsen-Wang Houdayer, pair and Jörg moves now update single-site clusters, so their trajectories differ from earlier builds.

Python

For a batteries-included Python interface, see peapods.

XY models