Struct IsingModel 

pub struct IsingModel {
    pub dim: usize,
    pub lx: usize,
    pub ly: usize,
    pub j_coupling: f64,
    pub field: f64,
    pub spins: Vec<i8>,
}

Ising model on a 1D or 2D lattice with Metropolis Monte Carlo.

Spins are stored as i8 values ±1. The Hamiltonian is H = -J Σ_{⟨i,j⟩} s_i s_j - h Σ_i s_i.

Fields

dim: usize

Lattice dimension (1 or 2).

lx: usize

Number of sites along each axis (Lx for 1D; Lx × Ly for 2D).

ly: usize

Number of sites along y-axis (only used for 2D; 1 for 1D).

j_coupling: f64

Coupling constant J (J > 0 → ferromagnetic).

field: f64

External magnetic field h.

spins: Vec<i8>

Spin configuration: +1 or -1.

Implementations

impl IsingModel

pub fn new_1d(n: usize, j_coupling: f64, field: f64) -> Self

Constructs a 1D Ising model with n sites, all spins +1.

pub fn new_2d(lx: usize, ly: usize, j_coupling: f64, field: f64) -> Self

Constructs a 2D Ising model (lx × ly lattice) with all spins +1.

pub fn randomise(&mut self, seed: u64)

Randomises the spin configuration using the given seed.

pub fn energy(&self) -> f64

Returns the total energy of the current configuration.

pub fn magnetisation(&self) -> f64

Returns the magnetisation per spin m = (1/N) Σ_i s_i.

pub fn metropolis_sweep(&mut self, n_sweeps: usize, temperature: f64, seed: u64)

Runs n_sweeps full Metropolis sweeps at temperature temperature.

Each sweep attempts one flip per spin.

pub fn susceptibility( &mut self, temperature: f64, n_eq: usize, n_samples: usize, seed: u64, ) -> f64

Returns the magnetic susceptibility χ = (⟨m²⟩ - ⟨m⟩²) N / T estimated over n_samples post-equilibration sweeps.

pub fn critical_temperature_1d_approx(&self) -> f64

Exact 1D critical temperature (returns J for reference; true T_c → 0 in 1D).

pub fn mean_field_tc_2d(&self) -> f64

Mean-field critical temperature for the 2D Ising model: T_c ≈ z J / (2 k_B). For a 2D square lattice z = 4.

pub fn onsager_tc(&self) -> f64

Exact Onsager critical temperature for the 2D square-lattice Ising model. T_c = 2J / ln(1 + √2).

Trait Implementations

impl Clone for IsingModel

fn clone(&self) -> IsingModel

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for IsingModel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.