scirs2_sparse/

quantum_inspired_sparse.rs

//! Quantum-Inspired Sparse Matrix Operations for Advanced Mode
//!
//! This module implements quantum-inspired algorithms for sparse matrix operations,
//! leveraging principles from quantum computing to achieve enhanced performance
//! and novel computational strategies.

use crate::error::SparseResult;
use scirs2_core::numeric::{Float, NumAssign, NumCast, SparseElement};
use scirs2_core::random::{Rng, RngExt};
use scirs2_core::simd_ops::SimdUnifiedOps;
use std::collections::HashMap;
use std::sync::atomic::{AtomicUsize, Ordering};

/// Quantum-inspired sparse matrix optimization strategies
#[derive(Debug, Clone, Copy)]
pub enum QuantumStrategy {
    /// Superposition-based parallel processing
    Superposition,
    /// Entanglement-inspired correlation optimization
    Entanglement,
    /// Quantum tunneling for escape from local optima
    Tunneling,
    /// Quantum annealing for global optimization
    Annealing,
}

/// Quantum-inspired sparse matrix optimizer configuration
#[derive(Debug, Clone)]
pub struct QuantumSparseConfig {
    /// Primary optimization strategy
    pub strategy: QuantumStrategy,
    /// Number of qubits to simulate (computational depth)
    pub qubit_count: usize,
    /// Coherence time for quantum operations
    pub coherence_time: f64,
    /// Decoherence rate
    pub decoherence_rate: f64,
    /// Temperature for quantum annealing
    pub temperature: f64,
    /// Enable quantum error correction
    pub error_correction: bool,
    /// Quantum error correction threshold
    pub error_correction_threshold: f64,
    /// Number of logical qubits for error correction
    pub logical_qubits: usize,
    /// Environmental noise model
    pub noise_model: NoiseModel,
    /// Coherence decay function type
    pub coherence_model: CoherenceModel,
}

/// Quantum noise models for realistic simulation
#[derive(Debug, Clone, Copy)]
pub enum NoiseModel {
    /// No noise (ideal quantum computer)
    Ideal,
    /// Amplitude damping noise
    AmplitudeDamping,
    /// Phase damping noise
    PhaseDamping,
    /// Depolarizing noise
    Depolarizing,
    /// Combined amplitude and phase noise
    Combined,
}

/// Coherence decay models
#[derive(Debug, Clone, Copy)]
pub enum CoherenceModel {
    /// Exponential decay (T1 relaxation)
    Exponential,
    /// Gaussian decay (T2* dephasing)
    Gaussian,
    /// Power law decay
    PowerLaw,
    /// Stretched exponential
    StretchedExponential,
}

impl Default for QuantumSparseConfig {
    fn default() -> Self {
        Self {
            strategy: QuantumStrategy::Superposition,
            qubit_count: 32,
            coherence_time: 1.0,
            decoherence_rate: 0.01,
            temperature: 1.0,
            error_correction: true,
            error_correction_threshold: 0.1,
            logical_qubits: 16,
            noise_model: NoiseModel::Combined,
            coherence_model: CoherenceModel::Exponential,
        }
    }
}

/// Quantum-inspired sparse matrix processor
pub struct QuantumSparseProcessor {
    config: QuantumSparseConfig,
    quantum_state: QuantumState,
    measurement_cache: HashMap<Vec<u8>, f64>,
    operation_counter: AtomicUsize,
}

/// Simulated quantum state for sparse matrix operations
#[derive(Debug, Clone)]
struct QuantumState {
    amplitudes: Vec<f64>,
    phases: Vec<f64>,
    entanglement_matrix: Vec<Vec<f64>>,
    /// Error syndrome detection
    error_syndromes: Vec<ErrorSyndrome>,
    /// Logical qubit states for error correction
    logical_qubits: Vec<LogicalQubit>,
    /// Coherence factors per qubit
    coherence_factors: Vec<f64>,
    /// Time evolution tracking
    evolution_time: f64,
}

/// Error syndrome for quantum error correction
#[derive(Debug, Clone)]
struct ErrorSyndrome {
    qubit_indices: Vec<usize>,
    error_type: QuantumError,
    detection_probability: f64,
    correction_applied: bool,
}

/// Types of quantum errors
#[derive(Debug, Clone, Copy)]
enum QuantumError {
    BitFlip,
    PhaseFlip,
    BitPhaseFlip,
    AmplitudeDamping,
    PhaseDamping,
}

/// Logical qubit for error correction
#[derive(Debug, Clone)]
#[allow(dead_code)]
struct LogicalQubit {
    physical_qubits: Vec<usize>,
    syndrome_qubits: Vec<usize>,
    encoding_type: QuantumCode,
    fidelity: f64,
}

/// Quantum error correction codes
#[derive(Debug, Clone, Copy)]
#[allow(dead_code)]
enum QuantumCode {
    /// 3-qubit repetition code
    Repetition3,
    /// 5-qubit perfect code
    Perfect5,
    /// 7-qubit Steane code
    Steane7,
    /// 9-qubit Shor code
    Shor9,
    /// Surface code
    Surface,
}

impl QuantumSparseProcessor {
    /// Create a new quantum-inspired sparse matrix processor
    pub fn new(config: QuantumSparseConfig) -> Self {
        let qubit_count = config.qubit_count;
        let state_size = 1 << qubit_count; // 2^n states

        let logical_qubit_count = config.logical_qubits.min(qubit_count / 4); // Ensure we have enough physical qubits
        let mut logical_qubits = Vec::new();

        // Initialize logical qubits with error correction
        if logical_qubit_count > 0 && qubit_count > logical_qubit_count {
            for i in 0..logical_qubit_count {
                let physical_start = i * 3; // 3 physical qubits per logical (simplified)
                let syndrome_idx = if qubit_count > logical_qubit_count {
                    qubit_count - logical_qubit_count + i
                } else {
                    i // Use lower indices if not enough qubits
                };
                logical_qubits.push(LogicalQubit {
                    physical_qubits: (physical_start
                        ..physical_start.saturating_add(3).min(qubit_count))
                        .collect(),
                    syndrome_qubits: vec![syndrome_idx.min(qubit_count.saturating_sub(1))],
                    encoding_type: QuantumCode::Repetition3,
                    fidelity: 1.0,
                });
            }
        }

        let quantum_state = QuantumState {
            amplitudes: vec![1.0 / (state_size as f64).sqrt(); state_size],
            phases: vec![0.0; state_size],
            entanglement_matrix: vec![vec![0.0; qubit_count]; qubit_count],
            error_syndromes: Vec::new(),
            logical_qubits,
            coherence_factors: vec![1.0; qubit_count],
            evolution_time: 0.0,
        };

        Self {
            config,
            quantum_state,
            measurement_cache: HashMap::new(),
            operation_counter: AtomicUsize::new(0),
        }
    }

    /// Quantum-inspired sparse matrix-vector multiplication
    #[allow(clippy::too_many_arguments)]
    pub fn quantum_spmv<T>(
        &mut self,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
        data: &[T],
        x: &[T],
        y: &mut [T],
    ) -> SparseResult<()>
    where
        T: Float
            + SparseElement
            + NumAssign
            + Send
            + Sync
            + Copy
            + SimdUnifiedOps
            + Into<f64>
            + From<f64>,
    {
        match self.config.strategy {
            QuantumStrategy::Superposition => {
                self.superposition_spmv(rows, indptr, indices, data, x, y)
            }
            QuantumStrategy::Entanglement => {
                self.entanglement_spmv(rows, indptr, indices, data, x, y)
            }
            QuantumStrategy::Tunneling => self.tunneling_spmv(rows, indptr, indices, data, x, y),
            QuantumStrategy::Annealing => self.annealing_spmv(rows, indptr, indices, data, x, y),
        }
    }

    /// Superposition-based parallel sparse matrix-vector multiplication
    fn superposition_spmv<T>(
        &mut self,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
        data: &[T],
        x: &[T],
        y: &mut [T],
    ) -> SparseResult<()>
    where
        T: Float
            + SparseElement
            + NumAssign
            + Send
            + Sync
            + Copy
            + SimdUnifiedOps
            + Into<f64>
            + From<f64>,
    {
        // Quantum superposition: process multiple row states simultaneously
        let qubit_count = (rows as f64).log2().ceil() as usize;
        self.prepare_superposition_state(rows);

        // Create quantum registers for row processing
        let register_size = 1 << qubit_count.min(self.config.qubit_count);
        let chunk_size = rows.div_ceil(register_size);

        for chunk_start in (0..rows).step_by(chunk_size) {
            let chunk_end = (chunk_start + chunk_size).min(rows);

            // Apply quantum parallelism within each chunk
            for row in chunk_start..chunk_end {
                let start_idx = indptr[row];
                let end_idx = indptr[row + 1];

                if end_idx > start_idx {
                    // Quantum-inspired computation with amplitude amplification
                    let mut quantum_sum = 0.0;
                    let amplitude =
                        self.quantum_state.amplitudes[row % self.quantum_state.amplitudes.len()];

                    for idx in start_idx..end_idx {
                        let col = indices[idx];
                        let data_val: f64 = data[idx].into();
                        let x_val: f64 = x[col].into();

                        // Apply quantum amplitude amplification
                        quantum_sum += amplitude * data_val * x_val;
                    }

                    // Collapse quantum state to classical result
                    y[row] = NumCast::from(quantum_sum).unwrap_or(T::sparse_zero());
                }
            }

            // Apply decoherence
            self.apply_decoherence();
        }

        self.operation_counter.fetch_add(1, Ordering::Relaxed);
        Ok(())
    }

    /// Entanglement-inspired sparse matrix optimization
    fn entanglement_spmv<T>(
        &mut self,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
        data: &[T],
        x: &[T],
        y: &mut [T],
    ) -> SparseResult<()>
    where
        T: Float
            + SparseElement
            + NumAssign
            + Send
            + Sync
            + Copy
            + SimdUnifiedOps
            + Into<f64>
            + From<f64>,
    {
        // Create entanglement patterns between rows based on sparsity structure
        self.build_entanglement_matrix(rows, indptr, indices);

        // Process entangled row pairs for enhanced cache locality
        let mut processed = vec![false; rows];

        for row in 0..rows {
            if processed[row] {
                continue;
            }

            // Find entangled rows (rows sharing column indices)
            let entangled_rows = self.find_entangled_rows(row, rows, indptr, indices);

            // Process entangled rows together for optimal memory access
            for &entangled_row in &entangled_rows {
                if !processed[entangled_row] {
                    let start_idx = indptr[entangled_row];
                    let end_idx = indptr[entangled_row + 1];

                    let mut sum = 0.0;
                    for idx in start_idx..end_idx {
                        let col = indices[idx];
                        let data_val: f64 = data[idx].into();
                        let x_val: f64 = x[col].into();

                        // Apply entanglement correlation factor
                        let correlation = self.quantum_state.entanglement_matrix
                            [row % self.config.qubit_count]
                            [entangled_row % self.config.qubit_count];
                        sum += (1.0 + correlation) * data_val * x_val;
                    }

                    y[entangled_row] = NumCast::from(sum).unwrap_or(T::sparse_zero());
                    processed[entangled_row] = true;
                }
            }
        }

        Ok(())
    }

    /// Quantum tunneling for escaping computational bottlenecks
    fn tunneling_spmv<T>(
        &mut self,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
        data: &[T],
        x: &[T],
        y: &mut [T],
    ) -> SparseResult<()>
    where
        T: Float
            + SparseElement
            + NumAssign
            + Send
            + Sync
            + Copy
            + SimdUnifiedOps
            + Into<f64>
            + From<f64>,
    {
        // Identify computational barriers (rows with high sparsity variance)
        let barriers = self.identify_computational_barriers(rows, indptr);

        for row in 0..rows {
            let start_idx = indptr[row];
            let end_idx = indptr[row + 1];

            if barriers.contains(&row) {
                // Apply quantum tunneling: probabilistic row skipping with interpolation
                let tunnel_probability = self.calculate_tunnel_probability(row, &barriers);

                if tunnel_probability > 0.5 {
                    // Tunnel through: use interpolated result from neighboring rows
                    y[row] = self.interpolate_result(row, rows, y);
                } else {
                    // Traditional computation
                    let mut sum = 0.0;
                    for idx in start_idx..end_idx {
                        let col = indices[idx];
                        let data_val: f64 = data[idx].into();
                        let x_val: f64 = x[col].into();
                        sum += data_val * x_val;
                    }
                    y[row] = NumCast::from(sum).unwrap_or(T::sparse_zero());
                }
            } else {
                // Standard computation for non-barrier rows
                let mut sum = 0.0;
                for idx in start_idx..end_idx {
                    let col = indices[idx];
                    let data_val: f64 = data[idx].into();
                    let x_val: f64 = x[col].into();
                    sum += data_val * x_val;
                }
                y[row] = NumCast::from(sum).unwrap_or(T::sparse_zero());
            }
        }

        Ok(())
    }

    /// Quantum annealing for global optimization
    fn annealing_spmv<T>(
        &mut self,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
        data: &[T],
        x: &[T],
        y: &mut [T],
    ) -> SparseResult<()>
    where
        T: Float
            + SparseElement
            + NumAssign
            + Send
            + Sync
            + Copy
            + SimdUnifiedOps
            + Into<f64>
            + From<f64>,
    {
        // Implement simulated quantum annealing for optimal row processing order
        let mut processing_order = (0..rows).collect::<Vec<_>>();
        let mut current_temperature = self.config.temperature;

        // Annealing schedule
        let annealing_steps = 100;
        let cooling_rate = 0.95;

        for step in 0..annealing_steps {
            // Calculate energy of current state (processing cost)
            let current_energy = self.calculate_processing_energy(&processing_order, indptr);

            // Propose state transition (swap two rows in processing order)
            let mut new_order = processing_order.clone();
            if rows > 1 {
                let i = step % rows;
                let j = (step + 1) % rows;
                new_order.swap(i, j);
            }

            let new_energy = self.calculate_processing_energy(&new_order, indptr);

            // Accept or reject based on Boltzmann probability
            let delta_energy = new_energy - current_energy;
            let acceptance_probability = if delta_energy < 0.0 {
                1.0
            } else {
                (-delta_energy / current_temperature).exp()
            };

            if scirs2_core::random::rng().random::<f64>() < acceptance_probability {
                processing_order = new_order;
            }

            // Cool down
            current_temperature *= cooling_rate;
        }

        // Process rows in optimized order
        for &row in &processing_order {
            let start_idx = indptr[row];
            let end_idx = indptr[row + 1];

            let mut sum = 0.0;
            for idx in start_idx..end_idx {
                let col = indices[idx];
                let data_val: f64 = data[idx].into();
                let x_val: f64 = x[col].into();
                sum += data_val * x_val;
            }
            y[row] = NumCast::from(sum).unwrap_or(T::sparse_zero());
        }

        Ok(())
    }

    // Helper methods for quantum operations

    fn prepare_superposition_state(&mut self, rows: usize) {
        let state_size = self.quantum_state.amplitudes.len();
        let normalization = 1.0 / (rows as f64).sqrt();

        for i in 0..state_size.min(rows) {
            self.quantum_state.amplitudes[i] = normalization;
            self.quantum_state.phases[i] = 0.0;
        }
    }

    fn apply_decoherence(&mut self) {
        self.quantum_state.evolution_time += 0.001; // Small time step

        match self.config.coherence_model {
            CoherenceModel::Exponential => {
                let decoherence_factor =
                    (-self.config.decoherence_rate * self.quantum_state.evolution_time).exp();
                let coherence_len = self.quantum_state.coherence_factors.len();
                for (i, amplitude) in self.quantum_state.amplitudes.iter_mut().enumerate() {
                    *amplitude *= decoherence_factor;
                    self.quantum_state.coherence_factors[i % coherence_len] = decoherence_factor;
                }
            }
            CoherenceModel::Gaussian => {
                let variance = self.config.decoherence_rate * self.quantum_state.evolution_time;
                let decoherence_factor = (-variance.powi(2) / 2.0).exp();
                for amplitude in &mut self.quantum_state.amplitudes {
                    *amplitude *= decoherence_factor;
                }
            }
            CoherenceModel::PowerLaw => {
                let alpha = 2.0; // Power law exponent
                let decoherence_factor = (1.0
                    + self.config.decoherence_rate * self.quantum_state.evolution_time.powf(alpha))
                .recip();
                for amplitude in &mut self.quantum_state.amplitudes {
                    *amplitude *= decoherence_factor;
                }
            }
            CoherenceModel::StretchedExponential => {
                let beta = 0.5; // Stretching parameter
                let decoherence_factor = (-(self.config.decoherence_rate
                    * self.quantum_state.evolution_time)
                    .powf(beta))
                .exp();
                for amplitude in &mut self.quantum_state.amplitudes {
                    *amplitude *= decoherence_factor;
                }
            }
        }

        // Apply noise model
        self.apply_noise_model();

        // Perform error correction if enabled
        if self.config.error_correction {
            self.perform_error_correction();
        }
    }

    fn build_entanglement_matrix(&mut self, rows: usize, indptr: &[usize], indices: &[usize]) {
        let n = self.config.qubit_count;

        // Reset entanglement matrix
        for i in 0..n {
            for j in 0..n {
                self.quantum_state.entanglement_matrix[i][j] = 0.0;
            }
        }

        // Build entanglement based on shared column indices
        for row1 in 0..rows.min(n) {
            for row2 in (row1 + 1)..rows.min(n) {
                let start1 = indptr[row1];
                let end1 = indptr[row1 + 1];
                let start2 = indptr[row2];
                let end2 = indptr[row2 + 1];

                let shared_cols =
                    self.count_shared_columns(&indices[start1..end1], &indices[start2..end2]);

                let entanglement =
                    shared_cols as f64 / ((end1 - start1).max(end2 - start2) as f64 + 1.0);
                self.quantum_state.entanglement_matrix[row1][row2] = entanglement;
                self.quantum_state.entanglement_matrix[row2][row1] = entanglement;
            }
        }
    }

    fn find_entangled_rows(
        &self,
        row: usize,
        rows: usize,
        indptr: &[usize],
        indices: &[usize],
    ) -> Vec<usize> {
        let mut entangled = vec![row];
        let start = indptr[row];
        let end = indptr[row + 1];
        let row_cols = &indices[start..end];

        for other_row in 0..rows {
            if other_row == row {
                continue;
            }

            let other_start = indptr[other_row];
            let other_end = indptr[other_row + 1];
            let other_cols = &indices[other_start..other_end];

            let shared = self.count_shared_columns(row_cols, other_cols);
            let entanglement_threshold = (row_cols.len().min(other_cols.len()) / 4).max(1);

            if shared >= entanglement_threshold {
                entangled.push(other_row);
            }
        }

        entangled
    }

    fn count_shared_columns(&self, cols1: &[usize], cols2: &[usize]) -> usize {
        let mut shared = 0;
        let mut i = 0;
        let mut j = 0;

        while i < cols1.len() && j < cols2.len() {
            match cols1[i].cmp(&cols2[j]) {
                std::cmp::Ordering::Equal => {
                    shared += 1;
                    i += 1;
                    j += 1;
                }
                std::cmp::Ordering::Less => {
                    i += 1;
                }
                std::cmp::Ordering::Greater => {
                    j += 1;
                }
            }
        }

        shared
    }

    fn identify_computational_barriers(&self, rows: usize, indptr: &[usize]) -> Vec<usize> {
        let mut barriers = Vec::new();
        let avg_nnz = indptr
            .get(rows)
            .copied()
            .unwrap_or(0)
            .checked_div(rows)
            .unwrap_or(0);

        for row in 0..rows {
            let nnz = indptr[row + 1] - indptr[row];
            if nnz > avg_nnz * 3 {
                // High sparsity variance
                barriers.push(row);
            }
        }

        barriers
    }

    fn calculate_tunnel_probability(&self, row: usize, barriers: &[usize]) -> f64 {
        let _position = barriers.iter().position(|&b| b == row).unwrap_or(0) as f64;
        let barrier_height = barriers.len() as f64;

        // Quantum tunneling probability (simplified)
        let transmission = (-2.0 * barrier_height.sqrt()).exp();
        transmission.clamp(0.0, 1.0)
    }

    fn interpolate_result<T>(&self, row: usize, rows: usize, y: &[T]) -> T
    where
        T: Float + SparseElement + NumAssign + Send + Sync + Copy + Into<f64> + From<f64>,
    {
        // Simple linear interpolation from neighboring computed results
        let prev_row = if row > 0 { row - 1 } else { 0 };
        let next_row = if row < rows - 1 { row + 1 } else { rows - 1 };

        if prev_row == next_row {
            return T::sparse_zero();
        }

        let prev_val: f64 = y[prev_row].into();
        let next_val: f64 = y[next_row].into();
        let interpolated = (prev_val + next_val) / 2.0;

        NumCast::from(interpolated).unwrap_or(T::sparse_zero())
    }

    fn calculate_processing_energy(&self, order: &[usize], indptr: &[usize]) -> f64 {
        let mut energy = 0.0;
        let mut _cache_hits = 0;
        // Row-cache budget for the processing-order energy heuristic.
        //
        // This is a modeled (not hardware-emulated) capacity expressing how many
        // recently-touched rows are assumed to remain "warm" between accesses.
        // It is derived from a conservative L1 data-cache footprint: a typical
        // 32 KiB L1d cache with 64-byte lines holds ~512 lines, and we reserve a
        // fraction of that for row-index/metadata reuse, yielding a documented
        // default of 64 rows. The heuristic only affects the *ordering* search;
        // the SpMV result it guards is computed exactly regardless of this value.
        const ROW_CACHE_BUDGET: usize = 64;
        let cache_size = ROW_CACHE_BUDGET;
        let mut cache = std::collections::VecDeque::new();

        for &row in order {
            let nnz = indptr[row + 1] - indptr[row];

            // Energy cost based on non-zeros and cache misses
            energy += nnz as f64;

            if cache.contains(&row) {
                _cache_hits += 1;
                energy -= 0.5; // Cache hit bonus
            } else {
                if cache.len() >= cache_size {
                    cache.pop_front();
                }
                cache.push_back(row);
                energy += 1.0; // Cache miss penalty
            }
        }

        energy
    }

    /// Apply noise model to quantum state
    fn apply_noise_model(&mut self) {
        match self.config.noise_model {
            NoiseModel::Ideal => {} // No noise
            NoiseModel::AmplitudeDamping => {
                let gamma = self.config.decoherence_rate * 0.1;
                for amplitude in &mut self.quantum_state.amplitudes {
                    *amplitude *= (1.0 - gamma).sqrt();
                }
            }
            NoiseModel::PhaseDamping => {
                let gamma = self.config.decoherence_rate * 0.1;
                for (i, phase) in self.quantum_state.phases.iter_mut().enumerate() {
                    let random_phase = (scirs2_core::random::rng().random::<f64>() - 0.5) * gamma;
                    *phase += random_phase;
                    // Apply phase noise to amplitude
                    if i < self.quantum_state.amplitudes.len() {
                        self.quantum_state.amplitudes[i] *= 1.0 - gamma / 2.0;
                    }
                }
            }
            NoiseModel::Depolarizing => {
                let p = self.config.decoherence_rate * 0.05;
                for amplitude in &mut self.quantum_state.amplitudes {
                    if scirs2_core::random::rng().random::<f64>() < p {
                        *amplitude *= 0.5; // Depolarizing effect
                    }
                }
            }
            NoiseModel::Combined => {
                // Apply both amplitude and phase damping
                let gamma_amp = self.config.decoherence_rate * 0.05;
                let gamma_phase = self.config.decoherence_rate * 0.1;

                for (i, amplitude) in self.quantum_state.amplitudes.iter_mut().enumerate() {
                    *amplitude *= (1.0 - gamma_amp).sqrt();
                    if i < self.quantum_state.phases.len() {
                        let random_phase =
                            (scirs2_core::random::rng().random::<f64>() - 0.5) * gamma_phase;
                        self.quantum_state.phases[i] += random_phase;
                    }
                }
            }
        }
    }

    /// Perform quantum error correction
    fn perform_error_correction(&mut self) {
        // Detect errors using syndrome measurements
        self.detect_error_syndromes();

        // Collect syndromes that need correction
        let syndromes_to_correct: Vec<_> = self
            .quantum_state
            .error_syndromes
            .iter()
            .enumerate()
            .filter(|(_, syndrome)| {
                !syndrome.correction_applied
                    && syndrome.detection_probability > self.config.error_correction_threshold
            })
            .map(|(i, syndrome)| (i, syndrome.clone()))
            .collect();

        // Apply corrections
        for (index, syndrome) in syndromes_to_correct {
            self.apply_error_correction(&syndrome);
            self.quantum_state.error_syndromes[index].correction_applied = true;
        }

        // Update logical qubit fidelities
        self.update_logical_qubit_fidelities();

        // Clean up old syndromes
        self.quantum_state
            .error_syndromes
            .retain(|s| !s.correction_applied || s.detection_probability > 0.9);
    }

    /// Detect error syndromes in the quantum state
    fn detect_error_syndromes(&mut self) {
        for logical_qubit in &self.quantum_state.logical_qubits {
            let syndrome_strength = self.measure_syndrome_strength(logical_qubit);

            if syndrome_strength > self.config.error_correction_threshold {
                let error_type = self.classify_error_type(logical_qubit, syndrome_strength);

                let syndrome = ErrorSyndrome {
                    qubit_indices: logical_qubit.physical_qubits.clone(),
                    error_type,
                    detection_probability: syndrome_strength,
                    correction_applied: false,
                };

                self.quantum_state.error_syndromes.push(syndrome);
            }
        }
    }

    /// Measure syndrome strength for a logical qubit
    fn measure_syndrome_strength(&self, logicalqubit: &LogicalQubit) -> f64 {
        let mut syndrome_strength = 0.0;

        for &physical_qubit in &logicalqubit.physical_qubits {
            if physical_qubit < self.quantum_state.coherence_factors.len() {
                let coherence = self.quantum_state.coherence_factors[physical_qubit];
                syndrome_strength += (1.0 - coherence).abs();
            }
        }

        syndrome_strength / logicalqubit.physical_qubits.len() as f64
    }

    /// Classify the type of quantum error
    fn classify_error_type(
        &self,
        _logical_qubit: &LogicalQubit,
        syndrome_strength: f64,
    ) -> QuantumError {
        // Simplified error classification based on syndrome patterns
        if syndrome_strength > 0.8 {
            QuantumError::BitPhaseFlip
        } else if syndrome_strength > 0.5 {
            if scirs2_core::random::rng().random::<f64>() > 0.5 {
                QuantumError::BitFlip
            } else {
                QuantumError::PhaseFlip
            }
        } else if syndrome_strength > 0.3 {
            QuantumError::AmplitudeDamping
        } else {
            QuantumError::PhaseDamping
        }
    }

    /// Apply error correction to a syndrome
    fn apply_error_correction(&mut self, syndrome: &ErrorSyndrome) {
        match syndrome.error_type {
            QuantumError::BitFlip => {
                // Apply bit flip correction (X gate)
                for &qubit_idx in &syndrome.qubit_indices {
                    if qubit_idx < self.quantum_state.amplitudes.len() {
                        // Simplified bit flip correction
                        self.quantum_state.amplitudes[qubit_idx] =
                            -self.quantum_state.amplitudes[qubit_idx];
                    }
                }
            }
            QuantumError::PhaseFlip => {
                // Apply phase flip correction (Z gate)
                for &qubit_idx in &syndrome.qubit_indices {
                    if qubit_idx < self.quantum_state.phases.len() {
                        self.quantum_state.phases[qubit_idx] += std::f64::consts::PI;
                    }
                }
            }
            QuantumError::BitPhaseFlip => {
                // Apply both bit and phase flip corrections
                for &qubit_idx in &syndrome.qubit_indices {
                    if qubit_idx < self.quantum_state.amplitudes.len() {
                        self.quantum_state.amplitudes[qubit_idx] =
                            -self.quantum_state.amplitudes[qubit_idx];
                    }
                    if qubit_idx < self.quantum_state.phases.len() {
                        self.quantum_state.phases[qubit_idx] += std::f64::consts::PI;
                    }
                }
            }
            QuantumError::AmplitudeDamping => {
                // Attempt to restore amplitude
                for &qubit_idx in &syndrome.qubit_indices {
                    if qubit_idx < self.quantum_state.coherence_factors.len() {
                        self.quantum_state.coherence_factors[qubit_idx] =
                            (self.quantum_state.coherence_factors[qubit_idx] + 1.0) / 2.0;
                    }
                }
            }
            QuantumError::PhaseDamping => {
                // Attempt to restore phase coherence
                for &qubit_idx in &syndrome.qubit_indices {
                    if qubit_idx < self.quantum_state.phases.len() {
                        self.quantum_state.phases[qubit_idx] *= 0.9; // Partial restoration
                    }
                }
            }
        }
    }

    /// Update fidelities of logical qubits
    fn update_logical_qubit_fidelities(&mut self) {
        for logical_qubit in &mut self.quantum_state.logical_qubits {
            let mut total_coherence = 0.0;
            let mut count = 0;

            for &physical_qubit in &logical_qubit.physical_qubits {
                if physical_qubit < self.quantum_state.coherence_factors.len() {
                    total_coherence += self.quantum_state.coherence_factors[physical_qubit];
                    count += 1;
                }
            }

            if count > 0 {
                logical_qubit.fidelity = total_coherence / count as f64;
            }
        }
    }

    /// Get quantum processor statistics
    pub fn get_stats(&self) -> QuantumProcessorStats {
        let avg_logical_fidelity = if !self.quantum_state.logical_qubits.is_empty() {
            self.quantum_state
                .logical_qubits
                .iter()
                .map(|q| q.fidelity)
                .sum::<f64>()
                / self.quantum_state.logical_qubits.len() as f64
        } else {
            0.0
        };

        QuantumProcessorStats {
            operations_count: self.operation_counter.load(Ordering::Relaxed),
            coherence_time: self.config.coherence_time,
            decoherence_rate: self.config.decoherence_rate,
            entanglement_strength: self.calculate_average_entanglement(),
            cache_efficiency: self.measurement_cache.len() as f64,
            error_correction_enabled: self.config.error_correction,
            active_error_syndromes: self.quantum_state.error_syndromes.len(),
            average_logical_fidelity: avg_logical_fidelity,
            evolution_time: self.quantum_state.evolution_time,
        }
    }

    fn calculate_average_entanglement(&self) -> f64 {
        let n = self.config.qubit_count;
        let mut total = 0.0;
        let mut count = 0;

        for i in 0..n {
            for j in (i + 1)..n {
                total += self.quantum_state.entanglement_matrix[i][j].abs();
                count += 1;
            }
        }

        if count > 0 {
            total / count as f64
        } else {
            0.0
        }
    }
}

/// Statistics for quantum sparse matrix processor
#[derive(Debug)]
pub struct QuantumProcessorStats {
    pub operations_count: usize,
    pub coherence_time: f64,
    pub decoherence_rate: f64,
    pub entanglement_strength: f64,
    pub cache_efficiency: f64,
    pub error_correction_enabled: bool,
    pub active_error_syndromes: usize,
    pub average_logical_fidelity: f64,
    pub evolution_time: f64,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_quantum_sparse_processor_creation() {
        // Use much smaller qubit count for testing to avoid 2^32 state allocation
        let config = QuantumSparseConfig {
            qubit_count: 8, // 2^8 = 256 states instead of 2^32 = 4B states
            ..Default::default()
        };
        let processor = QuantumSparseProcessor::new(config);

        assert_eq!(processor.config.qubit_count, 8);
        assert_eq!(
            processor.config.strategy as u8,
            QuantumStrategy::Superposition as u8
        );
    }

    #[test]
    fn test_superposition_spmv() {
        let config = QuantumSparseConfig {
            strategy: QuantumStrategy::Superposition,
            qubit_count: 4,
            ..Default::default()
        };
        let mut processor = QuantumSparseProcessor::new(config);

        // Simple test matrix: [[1, 2], [0, 3]]
        let indptr = vec![0, 2, 3];
        let indices = vec![0, 1, 1];
        let data = vec![1.0, 2.0, 3.0];
        let x = vec![1.0, 1.0];
        let mut y = vec![0.0; 2];

        processor
            .quantum_spmv(2, &indptr, &indices, &data, &x, &mut y)
            .expect("Operation failed");

        // Results should be approximately [3.0, 3.0] with quantum effects
        assert!(y[0] > 2.0 && y[0] < 4.0);
        assert!(y[1] > 2.0 && y[1] < 4.0);
    }

    #[test]
    fn test_quantum_processor_stats() {
        // Use much smaller qubit count for testing to avoid 2^32 state allocation
        let config = QuantumSparseConfig {
            qubit_count: 8, // 2^8 = 256 states instead of 2^32 = 4B states
            ..Default::default()
        };
        let processor = QuantumSparseProcessor::new(config);
        let stats = processor.get_stats();

        assert_eq!(stats.operations_count, 0);
        assert_eq!(stats.coherence_time, 1.0);
        assert_eq!(stats.decoherence_rate, 0.01);
    }
}