Struct PauliSum 

pub struct PauliSum<const W: usize> { /* private fields */ }

Weighted sum of Pauli strings, stored as structure-of-arrays columns partitioned into buckets by a GF(2)-linear hash.

Terms come in canonical order: bucket index ascending, then lexicographic (x, z) within a bucket, with no repeated key. A sum of at most 1024 terms built by crate::BuildAccumulator has one bucket and so is plain lex-sorted; a larger one interleaves buckets, so compare sums by key (Self::get), not by position.

Implementations

impl<const W: usize> PauliSum<W>

pub fn empty(num_qubits: usize) -> Self

Empty sum on num_qubits qubits, in a single bucket.

Panics

Panics in debug builds if num_qubits > 64 · W.

pub fn clear(&mut self)

Drop every term, keeping the hash and the bucket storage.

pub fn len(&self) -> usize

Total number of terms.

pub fn is_empty(&self) -> bool

true if the sum has no terms.

pub fn num_qubits(&self) -> usize

Number of qubits this sum acts on.

pub fn num_buckets(&self) -> usize

Number of buckets, 1 << hash().bits().

pub fn hash(&self) -> &Gf2Hash<W>

The partitioning hash.

pub fn iter( &self, ) -> impl Iterator<Item = (&[u64; W], &[u64; W], Complex64)> + '_

Iterate every term in canonical order, which is not globally key-sorted.

pub fn to_arrays(&self) -> (Vec<[u64; W]>, Vec<[u64; W]>, Vec<Complex64>)

Copy every term out as three parallel columns, in canonical order.

pub fn get(&self, x: &[u64; W], z: &[u64; W]) -> Option<Complex64>

Coefficient of the term with key (x, z), or None if absent.

pub fn identity_coefficient(&self) -> Complex64

Coefficient of the identity term, i.e. tr(O) / 2^n.

pub fn scale(&mut self, c: Complex64)

Multiply every coefficient by c in place.

pub fn retain( &mut self, f: impl Fn(&[u64; W], &[u64; W], Complex64) -> bool + Sync, )

Keep only the terms for which f(x, z, coeff) is true; f may run on several threads at once.

pub fn overlap(&self, other: &Self) -> Complex64

Hilbert-Schmidt overlap tr(self† · other) / 2ⁿ, i.e. Σ conj(aᵢ)·bᵢ over the keys the two sums share.

Panics

Panics if the two sums disagree about num_qubits.

pub fn add(&self, other: &Self) -> Self

Sum of two sums, partitioned as self; terms summing to exactly zero are dropped.

Panics

Panics if the two sums disagree about num_qubits.

impl<const W: usize> PauliSum<W>

pub fn expectation_product(&self, basis: &ProductBasis<W>) -> Complex64

Expectation value ⟨ψ|O|ψ⟩ in the product state basis; complex since O need not be Hermitian.

impl<const W: usize> PauliSum<W>

pub fn expectation_stabilizer(&self, state: &StabilizerState<W>) -> Complex64

Expectation value ⟨ψ|O|ψ⟩ in a stabilizer state; complex since O need not be Hermitian.

Panics

Panics if state.num_qubits() differs from Self::num_qubits.

Trait Implementations

impl<const W: usize> Clone for PauliSum<W>

fn clone(&self) -> PauliSum<W>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<const W: usize> Debug for PauliSum<W>

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

Formats the value using the given formatter.