Struct ScotchOptions 

pub struct ScotchOptions {
    pub compress: bool,
    pub compress_ratio: f64,
    pub amd_switch: u32,
    pub coarsen_floor: u32,
    pub n_sep_trials: u32,
    pub fm_move_cap: u32,
    pub fm_pass_cap: u32,
    pub max_imbalance: f64,
    pub node_refine: bool,
    pub seed: u64,
}

Tunable parameters for SCOTCH nested-dissection ordering.

Defaults mirror SCOTCH 7.0’s vertex-separation ordering defaults as documented in the audit of dev/plans/ordering-scotch.md: cmin = 100 (coarsening floor), amd_switch = 120, n_sep_trials = 5, fm_move_cap = 200, bal = 0.05, compress_ratio = 0.7, seed = 0xDEAD_BEEF.

S1 status: only compress and compress_ratio are consumed by shipped code. The remaining fields are defined at the S1 boundary so that the public type does not drift between milestones.

Fields

compress: bool

Apply graph compression before partitioning.

compress_ratio: f64

Compress only if n_compressed / n < compress_ratio (i.e., compress only when compression saves at least (1 - compress_ratio) * 100 % of vertices). SCOTCH uses 0.75; we follow the plan’s slightly more aggressive 0.7.

amd_switch: u32

Switch from recursive ND to AMD on subproblems with at most this many vertices (SCOTCH default: 120).

coarsen_floor: u32

Stop coarsening when the graph has fewer than this many vertices (SCOTCH cmin = 100 for vertex-separation contexts).

n_sep_trials: u32

Number of separator trials at each recursion level (SCOTCH default: 5).

fm_move_cap: u32

FM refinement: per-pass move cap (SCOTCH default: 200).

fm_pass_cap: u32

FM refinement: per-call pass cap. SCOTCH’s default is “passes until no improvement”; we clamp at 32 for bounded runtime.

max_imbalance: f64

Imbalance tolerance (SCOTCH default: 0.05).

node_refine: bool

Carry the node separator through uncoarsening and refine it at every level, instead of refining the 2-way bisection with halo FM and building the separator once at the finest level.

The old path optimised the wrong objective at every level: halo FM minimises an edge cut, and minimum edge cut and minimum vertex separator are different problems. feral-metis had the identical defect and fixing it there was worth 3.1x on a collocation KKT; the same measurement for this crate is in dev/research/scotch-kahip-node-separator-2026-09-18.md.

seed: u64

Deterministic RNG seed for coarsening matching.

Trait Implementations

impl Clone for ScotchOptions

fn clone(&self) -> ScotchOptions

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ScotchOptions

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

Formats the value using the given formatter.

impl Default for ScotchOptions

fn default() -> Self

Returns the “default value” for a type.