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//! Hypergraph product codes for quantum LDPC
use super::pauli::{Pauli, PauliString};
use super::stabilizer::StabilizerCode;
use crate::error::QuantRS2Result;
use scirs2_core::ndarray::Array2;
/// Hypergraph product codes for quantum LDPC
#[derive(Debug, Clone)]
pub struct HypergraphProductCode {
/// Number of physical qubits
pub n: usize,
/// Number of logical qubits
pub k: usize,
/// X-type stabilizers
pub x_stabilizers: Vec<PauliString>,
/// Z-type stabilizers
pub z_stabilizers: Vec<PauliString>,
}
impl HypergraphProductCode {
/// Create hypergraph product code from two classical codes
pub fn new(h1: Array2<u8>, h2: Array2<u8>) -> Self {
let (m1, n1) = h1.dim();
let (m2, n2) = h2.dim();
let n = n1 * m2 + m1 * n2;
let k = (n1 - m1) * (n2 - m2);
let mut x_stabilizers = Vec::new();
let mut z_stabilizers = Vec::new();
// X-type stabilizers: H1 ⊗ I2
for i in 0..m1 {
for j in 0..m2 {
let mut paulis = vec![Pauli::I; n];
// Apply H1 to first block
for l in 0..n1 {
if h1[[i, l]] == 1 {
paulis[l * m2 + j] = Pauli::X;
}
}
x_stabilizers.push(PauliString::new(paulis));
}
}
// Z-type stabilizers: I1 ⊗ H2^T
for i in 0..m1 {
for j in 0..m2 {
let mut paulis = vec![Pauli::I; n];
// Apply H2^T to second block
for l in 0..n2 {
if h2[[j, l]] == 1 {
paulis[n1 * m2 + i * n2 + l] = Pauli::Z;
}
}
z_stabilizers.push(PauliString::new(paulis));
}
}
Self {
n,
k,
x_stabilizers,
z_stabilizers,
}
}
/// Convert to stabilizer code representation
pub fn to_stabilizer_code(&self) -> QuantRS2Result<StabilizerCode> {
let mut stabilizers = self.x_stabilizers.clone();
stabilizers.extend(self.z_stabilizers.clone());
// Simplified logical operators
let logical_x = vec![PauliString::new(vec![Pauli::X; self.n])];
let logical_z = vec![PauliString::new(vec![Pauli::Z; self.n])];
StabilizerCode::new(
self.n,
self.k,
3, // Simplified distance
stabilizers,
logical_x,
logical_z,
)
}
}