Struct SparseAtomCode 

pub struct SparseAtomCode {
    pub active_mask: BitVec,
    pub weights: Vec<f64>,
}

Per-point sparse code over K candidate atoms.

Invariants (checked in debug builds):

• active_mask.len() == weights.len() == K.
• For any k with active_mask.get(k) == false, the value weights[k] is a nuisance — it must not influence reconstruction. Selection strategies that lower a weight to zero (e.g. an L¹-relaxed gate after thresholding) are responsible for clearing the corresponding mask bit and zeroing weights[k].

We do not require weights[k] >= 0; some strategies (entropic softmax, TopK projection) keep the simplex, while others (L¹-relaxed) only enforce non-negativity at the active-set step. The owning gate/selection layer (crate::assignment::SaeAssignment) documents which invariant it maintains.

Fields

active_mask: BitVec

Length-K bitmask of active atoms for this point.

weights: Vec<f64>

Length-K dense weight vector. Only entries at active indices are semantically meaningful.

Implementations

impl SparseAtomCode

pub fn empty(k_atoms: usize) -> Self

Cold-start: no atoms active, all weights zero.

pub fn k_atoms(&self) -> usize

Total number of candidate atoms K this code is sized for.

pub fn n_active(&self) -> usize

Cardinality of the active support |S_n|.

pub fn active_weight_sum(&self) -> f64

Sum of active weights. For simplex-projected codes this should be ≈ 1.

pub fn assign(&mut self, k: usize, w: f64)

Set the weight for atom k and mark it active.

pub fn deactivate(&mut self, k: usize)

Deactivate atom k and zero its stored weight.

pub fn effective_weights(&self) -> Array1<f64>

Materialize the effective weight vector (zeros at inactive indices) as an owned Array1. Useful for matmul-shaped downstream code.

Trait Implementations

impl Clone for SparseAtomCode

fn clone(&self) -> SparseAtomCode

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for SparseAtomCode

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

Formats the value using the given formatter.