Enum Preconditioner 

pub enum Preconditioner {
    Identity,
    Jacobi(JacobiPreconditioner),
    Ilu0(Ilu0Preconditioner),
}

Preconditioner M^{-1} ≈ A^{-1}, dispatched by enum (no trait objects).

A preconditioner turns a residual r into z = M^{-1} r, an approximate error, which the Krylov solvers use to accelerate convergence. Construct one from the system matrix with Preconditioner::jacobi or Preconditioner::ilu0, or use Preconditioner::identity for none.

Variants

Identity

No preconditioning: M = I, so z = r.

Jacobi(JacobiPreconditioner)

Diagonal (Jacobi) scaling: z = r / diag(A).

Ilu0(Ilu0Preconditioner)

ILU(0) incomplete factorisation: z = (LU)^{-1} r.

Implementations

impl Preconditioner

pub fn identity() -> Self

Identity preconditioner (M = I) — equivalent to no preconditioning.

pub fn jacobi(a: &LduMatrix) -> Self

Build a Jacobi (reciprocal-diagonal) preconditioner from a.

Cannot break down: a zero diagonal entry is treated as 1.0. The guaranteed-robust choice when ILU(0) is not warranted.

pub fn ilu0(a: &LduMatrix) -> Self

Build an ILU(0) preconditioner from a (same sparsity pattern as A).

A genuine incomplete LU factorisation with a small-pivot guard; see Ilu0Preconditioner. Typically far stronger than Jacobi on diagonally-dominant / mildly ill-conditioned systems.

pub fn apply(&self, r: &[f64], z: &mut [f64])

Apply the preconditioner: write z = M^{-1} r.

r and z must both have length n_cells. For Preconditioner::Identity this copies r into z.