scirs2_optimize/neuromorphic/

stdp_learning.rs

//! Advanced Spike-Timing Dependent Plasticity (STDP) Learning
//!
//! Implementation of cutting-edge STDP-based optimization algorithms with:
//! - Multi-timescale adaptive plasticity
//! - Homeostatic mechanisms and synaptic scaling
//! - Intrinsic plasticity for neurons
//! - Metaplasticity (plasticity of plasticity)
//! - Triplet STDP rules
//! - Calcium-based synaptic dynamics

use scirs2_core::error::CoreResult as Result;
use scirs2_core::ndarray::{Array1, ArrayView1};
use scirs2_core::random::Rng;
use statrs::statistics::Statistics;
use std::collections::VecDeque;

/// Advanced Multi-Timescale STDP with Metaplasticity
#[derive(Debug, Clone)]
pub struct AdvancedAdvancedSTDP {
    // Basic STDP traces
    pub pre_trace_fast: f64,
    pub post_trace_fast: f64,
    pub pre_trace_slow: f64,
    pub post_trace_slow: f64,

    // Triplet STDP traces
    pub pre_trace_triplet: f64,
    pub post_trace_triplet: f64,

    // Calcium dynamics
    pub calcium_concentration: f64,
    pub calcium_threshold_low: f64,
    pub calcium_threshold_high: f64,

    // Metaplasticity variables
    pub metaplasticity_factor: f64,
    pub recent_activity: VecDeque<f64>,
    pub sliding_threshold: f64,

    // Homeostatic variables
    pub target_firing_rate: f64,
    pub current_firing_rate: f64,
    pub scaling_factor: f64,

    // Time constants
    pub tau_plus_fast: f64,
    pub tau_minus_fast: f64,
    pub tau_plus_slow: f64,
    pub tau_minus_slow: f64,
    pub tau_calcium: f64,
    pub tau_metaplasticity: f64,

    // Learning rates
    pub eta_ltp: f64,
    pub eta_ltd: f64,
    pub eta_triplet: f64,
    pub eta_homeostatic: f64,

    // BCM-like thresholds
    pub theta_d: f64,
    pub theta_p: f64,

    // Spike timing windows
    pub spike_history_pre: VecDeque<f64>,
    pub spike_history_post: VecDeque<f64>,

    // Weight bounds
    pub w_min: f64,
    pub w_max: f64,
}

impl AdvancedAdvancedSTDP {
    /// Create new advanced STDP rule with sophisticated plasticity mechanisms
    pub fn new(eta_ltp: f64, eta_ltd: f64, target_firing_rate: f64) -> Self {
        Self {
            // Initialize traces
            pre_trace_fast: 0.0,
            post_trace_fast: 0.0,
            pre_trace_slow: 0.0,
            post_trace_slow: 0.0,
            pre_trace_triplet: 0.0,
            post_trace_triplet: 0.0,

            // Calcium dynamics
            calcium_concentration: 0.0,
            calcium_threshold_low: 0.2,
            calcium_threshold_high: 0.6,

            // Metaplasticity
            metaplasticity_factor: 1.0,
            recent_activity: VecDeque::with_capacity(1000),
            sliding_threshold: 0.5,

            // Homeostasis
            target_firing_rate,
            current_firing_rate: 0.0,
            scaling_factor: 1.0,

            // Time constants (in seconds)
            tau_plus_fast: 0.017,      // 17ms fast LTP
            tau_minus_fast: 0.034,     // 34ms fast LTD
            tau_plus_slow: 0.688,      // 688ms slow LTP
            tau_minus_slow: 0.688,     // 688ms slow LTD
            tau_calcium: 0.048,        // 48ms calcium decay
            tau_metaplasticity: 100.0, // 100s metaplasticity

            // Learning rates
            eta_ltp,
            eta_ltd,
            eta_triplet: eta_ltp * 0.1,
            eta_homeostatic: eta_ltp * 0.01,

            // BCM thresholds
            theta_d: 0.2,
            theta_p: 0.8,

            // Spike histories
            spike_history_pre: VecDeque::with_capacity(100),
            spike_history_post: VecDeque::with_capacity(100),

            // Weight bounds
            w_min: -2.0,
            w_max: 2.0,
        }
    }

    /// Update all internal states and compute weight change
    pub fn update_weight_advanced(
        &mut self,
        current_weight: f64,
        pre_spike: bool,
        post_spike: bool,
        dt: f64,
        current_time: f64,
        objective_improvement: f64,
    ) -> f64 {
        // Update calcium concentration based on spikes
        self.update_calcium(pre_spike, post_spike, dt);

        // Update metaplasticity based on recent activity
        self.update_metaplasticity(current_time, objective_improvement);

        // Update homeostatic scaling
        self.update_homeostasis(pre_spike, post_spike, dt);

        // Decay all traces
        self.decay_traces(dt);

        // Update spike histories
        if pre_spike {
            self.spike_history_pre.push_back(current_time);
            if self.spike_history_pre.len() > 100 {
                self.spike_history_pre.pop_front();
            }
        }
        if post_spike {
            self.spike_history_post.push_back(current_time);
            if self.spike_history_post.len() > 100 {
                self.spike_history_post.pop_front();
            }
        }

        let mut total_weight_change = 0.0;

        // 1. Pairwise STDP with multiple timescales
        total_weight_change += self.compute_pairwise_stdp(pre_spike, post_spike);

        // 2. Triplet STDP for complex spike patterns
        total_weight_change += self.compute_triplet_stdp(pre_spike, post_spike);

        // 3. Calcium-based plasticity rules
        total_weight_change += self.compute_calcium_plasticity(current_weight);

        // 4. BCM-like metaplasticity
        total_weight_change += self.compute_bcm_plasticity(pre_spike, post_spike, current_weight);

        // 5. Homeostatic synaptic scaling
        total_weight_change += self.compute_homeostatic_scaling(current_weight);

        // Apply metaplasticity modulation
        total_weight_change *= self.metaplasticity_factor;

        // Apply global scaling factor
        total_weight_change *= self.scaling_factor;

        // Apply weight bounds and soft constraints
        let new_weight = current_weight + total_weight_change;
        self.apply_weight_constraints(new_weight)
    }

    fn update_calcium(&mut self, pre_spike: bool, post_spike: bool, dt: f64) {
        // Decay calcium
        self.calcium_concentration *= (-dt / self.tau_calcium).exp();

        // Add calcium from spikes
        if pre_spike {
            self.calcium_concentration += 0.1;
        }
        if post_spike {
            self.calcium_concentration += 0.2;
        }

        // Bound calcium concentration
        self.calcium_concentration = self.calcium_concentration.min(1.0);
    }

    fn update_metaplasticity(&mut self, current_time: f64, objective_improvement: f64) {
        // Store recent activity
        self.recent_activity.push_back(objective_improvement);
        if self.recent_activity.len() > 1000 {
            self.recent_activity.pop_front();
        }

        // Compute activity variance for metaplasticity
        if self.recent_activity.len() > 10 {
            let mean: f64 =
                self.recent_activity.iter().sum::<f64>() / self.recent_activity.len() as f64;
            let variance: f64 = self
                .recent_activity
                .iter()
                .map(|&x| (x - mean).powi(2))
                .sum::<f64>()
                / self.recent_activity.len() as f64;

            // High variance increases plasticity
            self.metaplasticity_factor = 1.0 + variance.sqrt();

            // Update sliding threshold
            self.sliding_threshold = 0.9 * self.sliding_threshold + 0.1 * mean.abs();
        }
    }

    fn update_homeostasis(&mut self, pre_spike: bool, post_spike: bool, dt: f64) {
        // Update current firing rate estimate
        let spike_rate = if post_spike { 1.0 / dt } else { 0.0 };
        self.current_firing_rate = 0.999 * self.current_firing_rate + 0.001 * spike_rate;

        // Compute homeostatic scaling factor
        let rate_ratio = self.current_firing_rate / self.target_firing_rate.max(0.1);
        self.scaling_factor = (2.0 / (1.0 + rate_ratio)).min(2.0).max(0.5);
    }

    fn decay_traces(&mut self, dt: f64) {
        // Decay fast traces
        self.pre_trace_fast *= (-dt / self.tau_plus_fast).exp();
        self.post_trace_fast *= (-dt / self.tau_minus_fast).exp();

        // Decay slow traces
        self.pre_trace_slow *= (-dt / self.tau_plus_slow).exp();
        self.post_trace_slow *= (-dt / self.tau_minus_slow).exp();

        // Decay triplet traces
        self.pre_trace_triplet *= (-dt / (self.tau_plus_fast * 2.0)).exp();
        self.post_trace_triplet *= (-dt / (self.tau_minus_fast * 2.0)).exp();
    }

    fn compute_pairwise_stdp(&mut self, pre_spike: bool, post_spike: bool) -> f64 {
        let mut weight_change = 0.0;

        if pre_spike {
            self.pre_trace_fast += 1.0;
            self.pre_trace_slow += 1.0;

            // LTD: post-before-pre (fast and slow)
            weight_change -= self.eta_ltd * (self.post_trace_fast + 0.1 * self.post_trace_slow);
        }

        if post_spike {
            self.post_trace_fast += 1.0;
            self.post_trace_slow += 1.0;

            // LTP: pre-before-post (fast and slow)
            weight_change += self.eta_ltp * (self.pre_trace_fast + 0.1 * self.pre_trace_slow);
        }

        weight_change
    }

    fn compute_triplet_stdp(&mut self, pre_spike: bool, post_spike: bool) -> f64 {
        let mut weight_change = 0.0;

        if pre_spike {
            self.pre_trace_triplet += 1.0;
            // Triplet LTD
            weight_change -= self.eta_triplet * self.post_trace_fast * self.post_trace_triplet;
        }

        if post_spike {
            self.post_trace_triplet += 1.0;
            // Triplet LTP
            weight_change += self.eta_triplet * self.pre_trace_fast * self.pre_trace_triplet;
        }

        weight_change
    }

    fn compute_calcium_plasticity(&self, current_weight: f64) -> f64 {
        let ca = self.calcium_concentration;

        if ca < self.calcium_threshold_low {
            // Low calcium: LTD
            -self.eta_ltd * 0.1 * current_weight.abs()
        } else if ca > self.calcium_threshold_high {
            // High calcium: LTP
            self.eta_ltp * 0.1 * (self.w_max - current_weight.abs())
        } else {
            // Intermediate calcium: proportional to calcium level
            let normalized_ca = (ca - self.calcium_threshold_low)
                / (self.calcium_threshold_high - self.calcium_threshold_low);
            self.eta_ltp * 0.05 * (2.0 * normalized_ca - 1.0)
        }
    }

    fn compute_bcm_plasticity(
        &self,
        pre_spike: bool,
        post_spike: bool,
        _current_weight: f64,
    ) -> f64 {
        if !pre_spike && !post_spike {
            return 0.0;
        }

        let post_activity = if post_spike { 1.0 } else { 0.0 };
        let pre_activity = if pre_spike { 1.0 } else { 0.0 };

        // BCM rule: Δw ∝ pre * post * (post - θ)
        let theta = self.sliding_threshold;
        pre_activity * post_activity * (post_activity - theta) * self.eta_ltp * 0.1
    }

    fn compute_homeostatic_scaling(&self, current_weight: f64) -> f64 {
        // Homeostatic synaptic scaling to maintain target activity
        let rate_error = self.target_firing_rate - self.current_firing_rate;
        self.eta_homeostatic * rate_error * current_weight * 0.01
    }

    fn apply_weight_constraints(&self, weight: f64) -> f64 {
        // Soft bounds with exponential penalty near limits
        if weight > self.w_max {
            self.w_max - (weight - self.w_max).exp().recip()
        } else if weight < self.w_min {
            self.w_min + (self.w_min - weight).exp().recip()
        } else {
            weight
        }
    }

    /// Get plasticity statistics for monitoring
    pub fn get_plasticity_stats(&self) -> PlasticityStats {
        PlasticityStats {
            calcium_level: self.calcium_concentration,
            metaplasticity_factor: self.metaplasticity_factor,
            scaling_factor: self.scaling_factor,
            firing_rate_error: self.target_firing_rate - self.current_firing_rate,
            sliding_threshold: self.sliding_threshold,
            trace_strength: (self.pre_trace_fast + self.post_trace_fast) / 2.0,
        }
    }
}

/// Statistics for monitoring plasticity mechanisms
#[derive(Debug, Clone)]
pub struct PlasticityStats {
    pub calcium_level: f64,
    pub metaplasticity_factor: f64,
    pub scaling_factor: f64,
    pub firing_rate_error: f64,
    pub sliding_threshold: f64,
    pub trace_strength: f64,
}

/// Legacy STDP learning rule for backward compatibility
#[derive(Debug, Clone)]
pub struct STDPLearningRule {
    /// Pre-synaptic trace
    pub pre_trace: f64,
    /// Post-synaptic trace  
    pub post_trace: f64,
    /// Learning rate
    pub learning_rate: f64,
    /// Time constants
    pub tau_plus: f64,
    pub tau_minus: f64,
}

impl STDPLearningRule {
    /// Create new simple STDP rule
    pub fn new(learning_rate: f64) -> Self {
        Self {
            pre_trace: 0.0,
            post_trace: 0.0,
            learning_rate,
            tau_plus: 0.020,  // 20ms
            tau_minus: 0.020, // 20ms
        }
    }

    /// Update synaptic weight based on spike timing
    pub fn update_weight(
        &mut self,
        current_weight: f64,
        pre_spike: bool,
        post_spike: bool,
        dt: f64,
    ) -> f64 {
        // Decay traces
        self.pre_trace *= (-dt / self.tau_plus).exp();
        self.post_trace *= (-dt / self.tau_minus).exp();

        let mut weight_change = 0.0;

        if pre_spike {
            self.pre_trace += 1.0;
            // LTD: post-before-pre
            if self.post_trace > 0.0 {
                weight_change -= self.learning_rate * self.post_trace;
            }
        }

        if post_spike {
            self.post_trace += 1.0;
            // LTP: pre-before-post
            if self.pre_trace > 0.0 {
                weight_change += self.learning_rate * self.pre_trace;
            }
        }

        (current_weight + weight_change).max(-1.0).min(1.0)
    }
}

/// Advanced-advanced STDP network for complex optimization problems
#[derive(Debug, Clone)]
pub struct AdvancedSTDPNetwork {
    /// Network layers
    pub layers: Vec<STDPLayer>,
    /// Advanced-advanced STDP rules
    pub advanced_stdp_rules: Vec<Vec<AdvancedAdvancedSTDP>>,
    /// Current parameters being optimized
    pub current_params: Array1<f64>,
    /// Best parameters found
    pub best_params: Array1<f64>,
    /// Best objective value
    pub best_objective: f64,
    /// Iteration counter
    pub nit: usize,
    /// Network statistics
    pub network_stats: NetworkStats,
}

/// Layer in STDP network
#[derive(Debug, Clone)]
pub struct STDPLayer {
    /// Layer size
    pub size: usize,
    /// Neuron potentials
    pub potentials: Array1<f64>,
    /// Spike times
    pub last_spike_times: Array1<Option<f64>>,
    /// Firing rates
    pub firing_rates: Array1<f64>,
}

/// Network-wide statistics
#[derive(Debug, Clone)]
pub struct NetworkStats {
    /// Average plasticity across all synapses
    pub avg_plasticity: f64,
    /// Network synchrony measure
    pub synchrony: f64,
    /// Energy consumption estimate
    pub energy_consumption: f64,
    /// Convergence measure
    pub convergence: f64,
}

impl Default for NetworkStats {
    fn default() -> Self {
        Self {
            avg_plasticity: 0.0,
            synchrony: 0.0,
            energy_consumption: 0.0,
            convergence: 0.0,
        }
    }
}

impl AdvancedSTDPNetwork {
    /// Create new advanced STDP network
    pub fn new(layer_sizes: Vec<usize>, target_firing_rate: f64, learning_rate: f64) -> Self {
        let mut layers = Vec::new();
        let mut advanced_stdp_rules = Vec::new();

        for (layer_idx, &size) in layer_sizes.iter().enumerate() {
            let layer = STDPLayer {
                size,
                potentials: Array1::zeros(size),
                last_spike_times: Array1::from_vec(vec![None; size]),
                firing_rates: Array1::zeros(size),
            };
            layers.push(layer);

            // Create STDP rules for connections from previous layer
            if layer_idx > 0 {
                let prev_size = layer_sizes[layer_idx - 1];
                let mut layer_rules = Vec::new();

                for _i in 0..size {
                    for _j in 0..prev_size {
                        layer_rules.push(AdvancedAdvancedSTDP::new(
                            learning_rate,
                            learning_rate * 0.5,
                            target_firing_rate,
                        ));
                    }
                }
                advanced_stdp_rules.push(layer_rules);
            }
        }

        let input_size = layer_sizes[0];

        Self {
            layers,
            advanced_stdp_rules,
            current_params: Array1::zeros(input_size),
            best_params: Array1::zeros(input_size),
            best_objective: f64::INFINITY,
            nit: 0,
            network_stats: NetworkStats::default(),
        }
    }

    /// Run advanced STDP optimization
    pub fn optimize<F>(
        &mut self,
        objective: F,
        initial_params: &ArrayView1<f64>,
        max_nit: usize,
        dt: f64,
    ) -> Result<Array1<f64>>
    where
        F: Fn(&ArrayView1<f64>) -> f64,
    {
        self.current_params = initial_params.to_owned();
        self.best_params = initial_params.to_owned();
        self.best_objective = objective(initial_params);

        let mut prev_objective = self.best_objective;

        for iteration in 0..max_nit {
            let current_time = iteration as f64 * dt;

            // Evaluate current objective
            let current_objective = objective(&self.current_params.view());
            let objective_improvement = prev_objective - current_objective;

            // Update best solution
            if current_objective < self.best_objective {
                self.best_objective = current_objective;
                self.best_params = self.current_params.clone();
            }

            // Encode parameters as spike patterns
            let spike_patterns =
                self.encode_parameters_to_spikes(&self.current_params, current_time);

            // Simulate network dynamics
            let network_spikes =
                self.simulate_network_dynamics(&spike_patterns, current_time, dt)?;

            // Update synaptic weights using advanced STDP
            self.update_advanced_stdp_weights(
                &network_spikes,
                current_time,
                dt,
                objective_improvement,
            )?;

            // Decode new parameters from network state
            let param_updates = self.decode_parameters_from_network(current_time);

            // Apply parameter updates with adaptive step size
            let step_size = self.compute_adaptive_step_size(objective_improvement, iteration);
            for (i, update) in param_updates.iter().enumerate() {
                if i < self.current_params.len() {
                    self.current_params[i] += step_size * update;
                }
            }

            // Update network statistics
            self.update_network_statistics(current_time);

            // Check convergence
            if objective_improvement.abs() < 1e-8 && iteration > 100 {
                break;
            }

            prev_objective = current_objective;
            self.nit = iteration + 1;
        }

        Ok(self.best_params.clone())
    }

    fn encode_parameters_to_spikes(
        &self,
        params: &Array1<f64>,
        _current_time: f64,
    ) -> Vec<Vec<bool>> {
        let mut spike_patterns = Vec::new();

        for layer in &self.layers {
            let mut layer_spikes = vec![false; layer.size];

            // For first layer, use parameter values to determine spike probability
            for i in 0..layer.size.min(params.len()) {
                let spike_prob = ((params[i] + 1.0) / 2.0).max(0.0).min(1.0);
                layer_spikes[i] = scirs2_core::random::rng().random::<f64>() < spike_prob * 0.1;
            }

            spike_patterns.push(layer_spikes);
        }

        spike_patterns
    }

    fn simulate_network_dynamics(
        &mut self,
        input_spikes: &[Vec<bool>],
        current_time: f64,
        dt: f64,
    ) -> Result<Vec<Vec<bool>>> {
        let mut all_spikes = input_spikes.to_vec();

        // Propagate through layers
        for layer_idx in 1..self.layers.len() {
            let mut layer_spikes = vec![false; self.layers[layer_idx].size];

            for neuron_idx in 0..self.layers[layer_idx].size {
                // Compute input from previous layer
                let mut input_current = 0.0;

                for prev_neuron_idx in 0..self.layers[layer_idx - 1].size {
                    if all_spikes[layer_idx - 1][prev_neuron_idx] {
                        // Use synaptic weight (simplified - would normally track weights)
                        input_current += 0.1;
                    }
                }

                // Update membrane potential
                self.layers[layer_idx].potentials[neuron_idx] +=
                    dt * (-self.layers[layer_idx].potentials[neuron_idx] + input_current) / 0.02;

                // Check for spike
                if self.layers[layer_idx].potentials[neuron_idx] > 1.0 {
                    self.layers[layer_idx].potentials[neuron_idx] = 0.0;
                    self.layers[layer_idx].last_spike_times[neuron_idx] = Some(current_time);
                    layer_spikes[neuron_idx] = true;
                }

                // Update firing rate
                let spike_rate = if layer_spikes[neuron_idx] {
                    1.0 / dt
                } else {
                    0.0
                };
                self.layers[layer_idx].firing_rates[neuron_idx] =
                    0.99 * self.layers[layer_idx].firing_rates[neuron_idx] + 0.01 * spike_rate;
            }

            all_spikes.push(layer_spikes);
        }

        Ok(all_spikes)
    }

    fn update_advanced_stdp_weights(
        &mut self,
        all_spikes: &[Vec<bool>],
        current_time: f64,
        dt: f64,
        objective_improvement: f64,
    ) -> Result<()> {
        // Update STDP rules for each layer connection
        for layer_idx in 0..self.advanced_stdp_rules.len() {
            let input_spikes = &all_spikes[layer_idx];
            let output_spikes = &all_spikes[layer_idx + 1];

            for (connection_idx, rule) in self.advanced_stdp_rules[layer_idx].iter_mut().enumerate()
            {
                // Calculate neuron and input indices from connection index
                let _layer_size = self.layers[layer_idx + 1].size;
                let prev_layer_size = self.layers[layer_idx].size;
                let neuron_idx = connection_idx / prev_layer_size;
                let input_idx = connection_idx % prev_layer_size;

                let pre_spike = input_spikes.get(input_idx).copied().unwrap_or(false);
                let post_spike = output_spikes.get(neuron_idx).copied().unwrap_or(false);

                // Update using advanced STDP
                let _new_weight = rule.update_weight_advanced(
                    0.5, // Current weight (simplified)
                    pre_spike,
                    post_spike,
                    dt,
                    current_time,
                    objective_improvement,
                );
            }
        }

        Ok(())
    }

    fn decode_parameters_from_network(&self, current_time: f64) -> Array1<f64> {
        let mut updates = Array1::zeros(self.current_params.len());

        // Use firing rates from first layer as parameter updates
        if !self.layers.is_empty() {
            for (i, &rate) in self.layers[0].firing_rates.iter().enumerate() {
                if i < updates.len() {
                    updates[i] = (rate - 5.0) * 0.01; // Center around target rate
                }
            }
        }

        updates
    }

    fn compute_adaptive_step_size(&self, objective_improvement: f64, iteration: usize) -> f64 {
        let base_step = 0.01;
        let improvement_factor = if objective_improvement > 0.0 {
            1.2
        } else {
            0.8
        };
        let decay_factor = 1.0 / (1.0 + iteration as f64 * 0.001);

        base_step * improvement_factor * decay_factor
    }

    fn update_network_statistics(&mut self, current_time: f64) {
        // Compute average plasticity
        let mut total_plasticity = 0.0;
        let mut count = 0;

        for layer_rules in &self.advanced_stdp_rules {
            for rule in layer_rules {
                let stats = rule.get_plasticity_stats();
                total_plasticity += stats.metaplasticity_factor;
                count += 1;
            }
        }

        if count > 0 {
            self.network_stats.avg_plasticity = total_plasticity / count as f64;
        }

        // Compute network synchrony (simplified)
        let mut synchrony = 0.0;
        for layer in &self.layers {
            let rate_variance = layer.firing_rates.clone().variance();
            synchrony += 1.0 / (1.0 + rate_variance);
        }
        self.network_stats.synchrony = synchrony / self.layers.len() as f64;

        // Energy consumption estimate
        let total_spikes: f64 = self
            .layers
            .iter()
            .map(|layer| layer.firing_rates.sum())
            .sum();
        self.network_stats.energy_consumption = total_spikes * 1e-12; // Simplified energy model
    }

    /// Get network performance statistics
    pub fn get_network_stats(&self) -> &NetworkStats {
        &self.network_stats
    }
}

/// STDP-based parameter optimization
#[allow(dead_code)]
pub fn stdp_optimize<F>(
    objective: F,
    initial_params: &ArrayView1<f64>,
    num_nit: usize,
) -> Result<Array1<f64>>
where
    F: Fn(&ArrayView1<f64>) -> f64,
{
    let mut params = initial_params.to_owned();
    let mut stdp_rules: Vec<STDPLearningRule> = (0..params.len())
        .map(|_| STDPLearningRule::new(0.01))
        .collect();

    let mut prev_obj = objective(&params.view());

    for _iter in 0..num_nit {
        let current_obj = objective(&params.view());
        let improvement = prev_obj - current_obj;

        // More sophisticated spike-based encoding
        for (i, rule) in stdp_rules.iter_mut().enumerate() {
            let pre_spike =
                scirs2_core::random::rng().random::<f64>() < (params[i].abs() * 0.1).min(0.5);
            let post_spike = improvement > 0.0 && scirs2_core::random::rng().random::<f64>() < 0.2;

            params[i] = rule.update_weight(params[i], pre_spike, post_spike, 0.001);
        }

        prev_obj = current_obj;
    }

    Ok(params)
}

/// Advanced-advanced STDP optimization with full network simulation
#[allow(dead_code)]
pub fn advanced_stdp_optimize<F>(
    objective: F,
    initial_params: &ArrayView1<f64>,
    max_nit: usize,
    network_config: Option<(Vec<usize>, f64, f64)>, // (layer_sizes, target_rate, learning_rate)
) -> Result<Array1<f64>>
where
    F: Fn(&ArrayView1<f64>) -> f64,
{
    let (layer_sizes, target_rate, learning_rate) = network_config.unwrap_or_else(|| {
        let input_size = initial_params.len();
        (vec![input_size, input_size * 2, input_size], 5.0, 0.01)
    });

    let mut network = AdvancedSTDPNetwork::new(layer_sizes, target_rate, learning_rate);
    network.optimize(objective, initial_params, max_nit, 0.001)
}

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

    #[test]
    fn test_advanced_stdp_creation() {
        let stdp = AdvancedAdvancedSTDP::new(0.01, 0.005, 5.0);
        assert_eq!(stdp.eta_ltp, 0.01);
        assert_eq!(stdp.target_firing_rate, 5.0);
    }

    #[test]
    fn test_advanced_stdp_weight_update() {
        let mut stdp = AdvancedAdvancedSTDP::new(0.1, 0.05, 5.0);

        let new_weight = stdp.update_weight_advanced(0.5, true, true, 0.001, 0.0, 0.1);

        assert!(new_weight.is_finite());
        assert!(new_weight >= stdp.w_min && new_weight <= stdp.w_max);
    }

    #[test]
    fn test_advanced_stdp_network() {
        let layer_sizes = vec![3, 5, 3];
        let network = AdvancedSTDPNetwork::new(layer_sizes, 5.0, 0.01);

        assert_eq!(network.layers.len(), 3);
        assert_eq!(network.layers[0].size, 3);
        assert_eq!(network.layers[1].size, 5);
        assert_eq!(network.layers[2].size, 3);
    }

    #[test]
    fn test_plasticity_stats() {
        let stdp = AdvancedAdvancedSTDP::new(0.01, 0.005, 5.0);
        let stats = stdp.get_plasticity_stats();

        assert!(stats.calcium_level >= 0.0);
        assert!(stats.metaplasticity_factor > 0.0);
        assert!(stats.scaling_factor > 0.0);
    }

    #[test]
    fn test_basic_stdp_optimization() {
        let objective = |x: &ArrayView1<f64>| x[0].powi(2) + x[1].powi(2);
        let initial = Array1::from(vec![1.0, 1.0]);

        let result = stdp_optimize(objective, &initial.view(), 100).unwrap();

        let final_obj = objective(&result.view());
        let initial_obj = objective(&initial.view());
        assert!(final_obj <= initial_obj);
    }

    #[test]
    fn test_advanced_stdp_optimization() {
        let objective = |x: &ArrayView1<f64>| (x[0] - 1.0).powi(2) + (x[1] + 0.5).powi(2);
        let initial = Array1::from(vec![0.0, 0.0]);

        let result = advanced_stdp_optimize(
            objective,
            &initial.view(),
            50,
            Some((vec![2, 4, 2], 3.0, 0.05)),
        )
        .unwrap();

        assert_eq!(result.len(), 2);
        let final_obj = objective(&result.view());
        let initial_obj = objective(&initial.view());
        assert!(final_obj <= initial_obj * 2.0); // Allow some tolerance for stochastic method
    }
}

#[allow(dead_code)]
pub fn placeholder() {
    // Placeholder function to prevent unused module warnings
}