Struct RK4Integrator 

pub struct RK4Integrator {
    pub atol: f64,
    pub rtol: f64,
}

Classic 4th-order Runge-Kutta integrator with optional adaptive step size.

In fixed-step mode each call to RK4Integrator::step advances the state by exactly dt. The adaptive driver RK4Integrator::integrate_adaptive doubles or halves the step based on an embedded 2nd-order (midpoint) error estimate.

Fields

atol: f64

Absolute tolerance used by the adaptive driver.

rtol: f64

Relative tolerance used by the adaptive driver.

Implementations

impl RK4Integrator

pub fn new(atol: f64, rtol: f64) -> Self

Construct an integrator with the given tolerances.

pub fn default_tolerances() -> Self

Construct with default tolerances (1e-6 absolute, 1e-6 relative).

pub fn step<F>(&self, s: &OdeState, dt: f64, f: &F) -> OdeState

where F: Fn(f64, &[f64]) -> Vec<f64>,

Perform one fixed RK4 step from state s using step size dt.

f(t, y) is the right-hand side of dy/dt = f(t, y).

pub fn integrate<F>( &self, s0: &OdeState, t_end: f64, dt: f64, f: &F, ) -> Vec<OdeState>

where F: Fn(f64, &[f64]) -> Vec<f64>,

Integrate from s0 to time t_end using a fixed step dt.

Returns all intermediate states including the initial state.

pub fn integrate_adaptive<F>( &self, s0: &OdeState, t_end: f64, dt_init: f64, f: &F, ) -> Vec<OdeState>

where F: Fn(f64, &[f64]) -> Vec<f64>,

Integrate from s0 to t_end with adaptive step size.

Uses an embedded RK2 error estimate to control the step. The step is accepted when the RMS error is below atol + rtol * ||y||.