Module truncation 

TruncationPolicy<W> — composable per-term and per-layer term filters.

The split between TruncationPolicy::keep_term (hot, per-output, must inline) and TruncationPolicy::finalize_layer (cold, once per layer, may be non-local) is performance-critical: keep_term runs millions of times per layer, finalize_layer runs once.

Both methods have default no-op implementations, so a policy only needs to override the one it uses. Compose two policies with And (both must accept) or Or (either accepts).

Built-ins: CoefficientThreshold drops terms below a magnitude; WeightCutoff drops terms above a Pauli weight; TopN keeps the n largest-magnitude terms via a layer-finalization partial sort.

See design doc §7.

Examples

use paulistrings::truncation::{And, CoefficientThreshold, WeightCutoff};
use paulistrings::TruncationPolicy;
use num_complex::Complex64;

// Keep terms with |coeff| > 1e-9 AND weight ≤ 4.
let policy = And(CoefficientThreshold(1e-9), WeightCutoff(4));

// A weight-1 term with coeff 0.5: passes both.
assert!(<_ as TruncationPolicy<1>>::keep_term(
    &policy, &[1], &[0], Complex64::new(0.5, 0.0),
));

Re-exports

pub use builtin::And;

pub use builtin::CoefficientThreshold;

pub use builtin::Or;

pub use builtin::TopN;

pub use builtin::WeightCutoff;

Modules

builtin

Built-in truncation policies and combinators. See design doc §7.

Traits

TruncationPolicy

A truncation strategy. Both methods have sensible defaults so users only implement the one they need.