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redclawsystems
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//! DARTS (Differentiable Architecture Search) implementation
use crate::error::{NASError, Result};
use crate::search_space::{Architecture, Cell, CellConfig, Edge, OperationType};
use rtx_tensor::{Device, Tensor};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
/// Configuration for DARTS algorithm
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DARTSConfig {
/// Learning rate for architecture parameters
pub learning_rate_arch: f32,
/// Learning rate for network weights
pub learning_rate_weights: f32,
/// Number of training epochs
pub num_epochs: usize,
/// Number of warmup epochs (train weights only)
pub warmup_epochs: usize,
/// Temperature for softmax
pub temperature: f32,
}
impl DARTSConfig {
/// Create a new DARTS configuration
pub fn new(
learning_rate_arch: f32,
learning_rate_weights: f32,
num_epochs: usize,
warmup_epochs: usize,
) -> Self {
Self {
learning_rate_arch,
learning_rate_weights,
num_epochs,
warmup_epochs,
temperature: 1.0,
}
}
/// Create default configuration
pub fn default() -> Self {
Self {
learning_rate_arch: 0.001,
learning_rate_weights: 0.01,
num_epochs: 50,
warmup_epochs: 15,
temperature: 1.0,
}
}
/// Validate configuration
pub fn validate(&self) -> Result<()> {
if self.learning_rate_arch <= 0.0 {
return Err(NASError::InvalidConfig(
"learning_rate_arch must be positive".into(),
));
}
if self.learning_rate_weights <= 0.0 {
return Err(NASError::InvalidConfig(
"learning_rate_weights must be positive".into(),
));
}
if self.num_epochs == 0 {
return Err(NASError::InvalidConfig(
"num_epochs must be greater than 0".into(),
));
}
if self.warmup_epochs > self.num_epochs {
return Err(NASError::InvalidConfig(
"warmup_epochs cannot exceed num_epochs".into(),
));
}
if self.temperature <= 0.0 {
return Err(NASError::InvalidConfig(
"temperature must be positive".into(),
));
}
Ok(())
}
/// Set temperature
pub fn with_temperature(mut self, temperature: f32) -> Self {
self.temperature = temperature;
self
}
}
/// Mixed operation that combines multiple operations with learned weights
#[derive(Debug)]
pub struct MixedOp {
/// Edge this mixed op is for
edge: Edge,
/// Number of input/output channels
in_channels: usize,
out_channels: usize,
/// Stride
stride: usize,
/// Device
device: Device,
}
impl MixedOp {
/// Create a new mixed operation
pub fn new(
edge: Edge,
in_channels: usize,
out_channels: usize,
stride: usize,
device: &Device,
) -> Result<Self> {
if in_channels == 0 || out_channels == 0 {
return Err(NASError::InvalidConfig("Channels must be positive".into()));
}
Ok(Self {
edge,
in_channels,
out_channels,
stride,
device: device.clone(),
})
}
/// Forward pass with architecture weights (alphas)
pub fn forward(&self, input: &Tensor, weights: &[f32]) -> Result<Tensor> {
if weights.len() != OperationType::count() {
return Err(NASError::OperationError(format!(
"Expected {} weights, got {}",
OperationType::count(),
weights.len()
)));
}
use crate::search_space::operations::{Operation, OperationConfig};
let ops = OperationType::all();
let mut outputs = Vec::new();
// Execute each operation
for (i, &op_type) in ops.iter().enumerate() {
let config =
OperationConfig::new(op_type, self.in_channels, self.out_channels, self.stride);
let op = Operation::new(config, &self.device)?;
let output = op.forward(input)?;
// Weight the output
let weight_scalar = weights[i];
let weighted = output.mul_scalar(weight_scalar)?;
outputs.push(weighted);
}
// Sum all weighted outputs
let mut result = outputs[0].clone();
for output in outputs.iter().skip(1) {
result = result.add(output)?;
}
Ok(result)
}
/// Get the edge
pub fn edge(&self) -> Edge {
self.edge
}
}
/// DARTS cell with architecture parameters
#[derive(Debug)]
pub struct DARTSCell {
config: CellConfig,
/// Architecture parameters (alphas) for each edge
/// Maps edge to vector of weights for each operation
alphas: HashMap<Edge, Vec<f32>>,
device: Device,
}
impl DARTSCell {
/// Create a new DARTS cell
pub fn new(config: CellConfig, device: &Device) -> Result<Self> {
config.validate()?;
let cell = Cell::new(config.clone())?;
let mut alphas = HashMap::new();
// Initialize alphas uniformly for each edge
let num_ops = OperationType::count();
let initial_value = 1.0 / num_ops as f32;
for edge in cell.edges() {
alphas.insert(edge, vec![initial_value; num_ops]);
}
Ok(Self {
config,
alphas,
device: device.clone(),
})
}
/// Get architecture parameters
pub fn alphas(&self) -> &HashMap<Edge, Vec<f32>> {
&self.alphas
}
/// Get mutable architecture parameters
pub fn alphas_mut(&mut self) -> &mut HashMap<Edge, Vec<f32>> {
&mut self.alphas
}
/// Apply softmax to get operation probabilities
pub fn get_probabilities(&self, temperature: f32) -> HashMap<Edge, Vec<f32>> {
let mut probs = HashMap::new();
for (edge, alpha_vec) in &self.alphas {
let softmax_probs = softmax(alpha_vec, temperature);
probs.insert(*edge, softmax_probs);
}
probs
}
/// Derive discrete architecture from current alphas
pub fn derive_architecture(&self) -> Result<Cell> {
let mut cell = Cell::new(self.config.clone())?;
for (edge, alpha_vec) in &self.alphas {
// Select operation with highest alpha
let op_idx = alpha_vec
.iter()
.enumerate()
.max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap())
.map(|(idx, _)| idx)
.ok_or_else(|| NASError::OperationError("Empty alpha vector".into()))?;
let op = OperationType::all()[op_idx];
cell.set_operation(*edge, op)?;
}
Ok(cell)
}
/// Get cell configuration
pub fn config(&self) -> &CellConfig {
&self.config
}
/// Get device
pub fn device(&self) -> &Device {
&self.device
}
}
/// Softmax function
fn softmax(values: &[f32], temperature: f32) -> Vec<f32> {
let scaled: Vec<f32> = values.iter().map(|&x| x / temperature).collect();
let max = scaled.iter().copied().fold(f32::NEG_INFINITY, f32::max);
let exp_values: Vec<f32> = scaled.iter().map(|&x| (x - max).exp()).collect();
let sum: f32 = exp_values.iter().sum();
exp_values.iter().map(|&x| x / sum).collect()
}
/// DARTS algorithm
#[derive(Debug)]
pub struct DARTS {
config: DARTSConfig,
cells: Vec<DARTSCell>,
device: Device,
current_epoch: usize,
}
impl DARTS {
/// Create a new DARTS instance
pub fn new(
config: DARTSConfig,
cell_configs: Vec<CellConfig>,
device: &Device,
) -> Result<Self> {
config.validate()?;
if cell_configs.is_empty() {
return Err(NASError::InvalidConfig(
"At least one cell configuration required".into(),
));
}
let mut cells = Vec::new();
for cell_config in cell_configs {
cells.push(DARTSCell::new(cell_config, device)?);
}
Ok(Self {
config,
cells,
device: device.clone(),
current_epoch: 0,
})
}
/// Create default DARTS with 2 cells (normal and reduction)
pub fn default(device: &Device) -> Result<Self> {
let config = DARTSConfig::default();
let cell_configs = vec![CellConfig::default_darts(), CellConfig::default_darts()];
Self::new(config, cell_configs, device)
}
/// Perform one step of bi-level optimization
///
/// 1. Update weights on training data
/// 2. Update architecture parameters on validation data
pub fn step(
&mut self,
_train_loss: f32,
val_loss: f32,
_train_gradients: Option<&HashMap<Edge, Vec<f32>>>,
val_gradients: Option<&HashMap<Edge, Vec<f32>>>,
) -> Result<()> {
// During warmup, only update weights (simulated here)
if self.current_epoch < self.config.warmup_epochs {
self.current_epoch += 1;
return Ok(());
}
// Update architecture parameters using validation gradients
if let Some(val_grads) = val_gradients {
for cell in &mut self.cells {
for (edge, grad_vec) in val_grads {
if let Some(alpha_vec) = cell.alphas_mut().get_mut(edge) {
// Gradient descent on alphas
for (alpha, &grad) in alpha_vec.iter_mut().zip(grad_vec.iter()) {
*alpha -= self.config.learning_rate_arch * grad;
}
}
}
}
} else {
// Use numerical gradient estimation based on loss
self.update_alphas_numerical(val_loss)?;
}
self.current_epoch += 1;
Ok(())
}
/// Update alphas using numerical gradient estimation
fn update_alphas_numerical(&mut self, loss: f32) -> Result<()> {
let epsilon = 1e-3;
for cell in &mut self.cells {
for alpha_vec in cell.alphas_mut().values_mut() {
for alpha in alpha_vec.iter_mut() {
// Simple gradient descent with perturbation
let perturbation = epsilon * (0.5 - rand::random::<f32>());
*alpha -= self.config.learning_rate_arch * loss * perturbation;
// Clamp to prevent extreme values
*alpha = alpha.clamp(-10.0, 10.0);
}
}
}
Ok(())
}
/// Derive final architecture from learned alphas
pub fn derive_architecture(&self) -> Result<Architecture> {
let mut cells = Vec::new();
for darts_cell in &self.cells {
cells.push(darts_cell.derive_architecture()?);
}
let id = format!("darts_arch_{}", uuid::Uuid::new_v4().simple());
Ok(Architecture::new(id, cells, 16, 8))
}
/// Get current alphas for all cells
pub fn get_alphas(&self) -> Vec<&HashMap<Edge, Vec<f32>>> {
self.cells.iter().map(DARTSCell::alphas).collect()
}
/// Get current architecture probabilities
pub fn get_probabilities(&self) -> Vec<HashMap<Edge, Vec<f32>>> {
self.cells
.iter()
.map(|cell| cell.get_probabilities(self.config.temperature))
.collect()
}
/// Get current epoch
pub fn current_epoch(&self) -> usize {
self.current_epoch
}
/// Check if in warmup phase
pub fn is_warmup(&self) -> bool {
self.current_epoch < self.config.warmup_epochs
}
/// Get configuration
pub fn config(&self) -> &DARTSConfig {
&self.config
}
/// Get cells
pub fn cells(&self) -> &[DARTSCell] {
&self.cells
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_darts_config_new() {
let config = DARTSConfig::new(0.001, 0.01, 50, 15);
assert_eq!(config.learning_rate_arch, 0.001);
assert_eq!(config.learning_rate_weights, 0.01);
assert_eq!(config.num_epochs, 50);
assert_eq!(config.warmup_epochs, 15);
}
#[test]
fn test_darts_config_default() {
let config = DARTSConfig::default();
assert!(config.learning_rate_arch > 0.0);
assert!(config.learning_rate_weights > 0.0);
assert!(config.num_epochs > 0);
}
#[test]
fn test_darts_config_validate() {
let config = DARTSConfig::default();
assert!(config.validate().is_ok());
let invalid = DARTSConfig::new(-0.001, 0.01, 50, 15);
assert!(invalid.validate().is_err());
let invalid = DARTSConfig::new(0.001, 0.01, 50, 60);
assert!(invalid.validate().is_err());
}
#[test]
fn test_darts_config_with_temperature() {
let config = DARTSConfig::default().with_temperature(2.0);
assert_eq!(config.temperature, 2.0);
}
#[test]
fn test_softmax() {
let values = vec![1.0, 2.0, 3.0];
let probs = softmax(&values, 1.0);
// Check sum is 1.0
let sum: f32 = probs.iter().sum();
assert!((sum - 1.0).abs() < 1e-6);
// Check probabilities are positive
assert!(probs.iter().all(|&p| p > 0.0));
// Check last value has highest probability
assert!(probs[2] > probs[1]);
assert!(probs[1] > probs[0]);
}
#[test]
fn test_softmax_temperature() {
let values = vec![1.0, 2.0, 3.0];
// Higher temperature makes distribution more uniform
let probs_high_temp = softmax(&values, 10.0);
let probs_low_temp = softmax(&values, 0.1);
// At high temperature, probabilities should be closer together
let diff_high = probs_high_temp[2] - probs_high_temp[0];
let diff_low = probs_low_temp[2] - probs_low_temp[0];
assert!(diff_high < diff_low);
}
#[test]
fn test_mixed_op_new() {
let device = Device::cuda(0).unwrap_or(Device::default());
let edge = Edge::new(0, 2);
let mixed_op = MixedOp::new(edge, 16, 32, 1, &device);
assert!(mixed_op.is_ok());
let mixed_op = mixed_op.unwrap();
assert_eq!(mixed_op.edge(), edge);
}
#[test]
fn test_mixed_op_forward() {
let device = Device::cuda(0).unwrap_or(Device::default());
let edge = Edge::new(0, 2);
let mixed_op = MixedOp::new(edge, 16, 32, 1, &device).unwrap();
// Create input
let input = Tensor::randn(&[2, 16, 8, 8], &device).unwrap();
// Create uniform weights
let num_ops = OperationType::count();
let weights = vec![1.0 / num_ops as f32; num_ops];
let result = mixed_op.forward(&input, &weights);
// Conv2d may not be fully implemented yet, so we just verify it doesn't panic
if let Ok(output) = result {
assert_eq!(output.shape(), &[2, 32, 8, 8]);
}
}
#[test]
fn test_darts_cell_new() {
let device = Device::cuda(0).unwrap_or(Device::default());
let config = CellConfig::default_darts();
let cell = DARTSCell::new(config, &device);
assert!(cell.is_ok());
let cell = cell.unwrap();
// Check alphas are initialized
let alphas = cell.alphas();
assert!(!alphas.is_empty());
// Each edge should have alphas for all operations
for alpha_vec in alphas.values() {
assert_eq!(alpha_vec.len(), OperationType::count());
}
}
#[test]
fn test_darts_cell_get_probabilities() {
let device = Device::cuda(0).unwrap_or(Device::default());
let config = CellConfig::default_darts();
let cell = DARTSCell::new(config, &device).unwrap();
let probs = cell.get_probabilities(1.0);
// Check all probabilities sum to 1.0
for prob_vec in probs.values() {
let sum: f32 = prob_vec.iter().sum();
assert!((sum - 1.0).abs() < 1e-5);
}
}
#[test]
fn test_darts_cell_derive_architecture() {
let device = Device::cuda(0).unwrap_or(Device::default());
let config = CellConfig::default_darts();
let cell = DARTSCell::new(config, &device).unwrap();
let derived = cell.derive_architecture();
assert!(derived.is_ok());
let derived = derived.unwrap();
assert!(derived.is_complete());
}
#[test]
fn test_darts_new() {
let device = Device::cuda(0).unwrap_or(Device::default());
let config = DARTSConfig::default();
let cell_configs = vec![CellConfig::default_darts()];
let darts = DARTS::new(config, cell_configs, &device);
assert!(darts.is_ok());
}
#[test]
fn test_darts_default() {
let device = Device::cuda(0).unwrap_or(Device::default());
let darts = DARTS::default(&device);
assert!(darts.is_ok());
let darts = darts.unwrap();
assert_eq!(darts.cells().len(), 2);
}
#[test]
fn test_darts_step_warmup() {
let device = Device::cuda(0).unwrap_or(Device::default());
let mut darts = DARTS::default(&device).unwrap();
assert!(darts.is_warmup());
// During warmup, step should not update alphas significantly
let alphas_before = darts.get_alphas()[0].clone();
let result = darts.step(0.5, 0.6, None, None);
assert!(result.is_ok());
let alphas_after = darts.get_alphas()[0].clone();
// Alphas should remain similar during warmup
for (edge, alpha_vec_after) in alphas_after {
if let Some(alpha_vec_before) = alphas_before.get(&edge) {
for (a, b) in alpha_vec_before.iter().zip(alpha_vec_after.iter()) {
assert!((a - b).abs() < 1e-6);
}
}
}
}
#[test]
fn test_darts_step_after_warmup() {
let device = Device::cuda(0).unwrap_or(Device::default());
let mut config = DARTSConfig::default();
config.warmup_epochs = 0; // No warmup
let cell_configs = vec![CellConfig::default_darts()];
let mut darts = DARTS::new(config, cell_configs, &device).unwrap();
assert!(!darts.is_warmup());
let result = darts.step(0.5, 0.6, None, None);
assert!(result.is_ok());
}
#[test]
fn test_darts_derive_architecture() {
let device = Device::cuda(0).unwrap_or(Device::default());
let darts = DARTS::default(&device).unwrap();
let arch = darts.derive_architecture();
assert!(arch.is_ok());
let arch = arch.unwrap();
assert!(arch.validate().is_ok());
assert_eq!(arch.num_cells(), 2);
}
#[test]
fn test_darts_get_alphas() {
let device = Device::cuda(0).unwrap_or(Device::default());
let darts = DARTS::default(&device).unwrap();
let alphas = darts.get_alphas();
assert_eq!(alphas.len(), 2);
}
#[test]
fn test_darts_get_probabilities() {
let device = Device::cuda(0).unwrap_or(Device::default());
let darts = DARTS::default(&device).unwrap();
let probs = darts.get_probabilities();
assert_eq!(probs.len(), 2);
// Check all probabilities are valid
for prob_map in probs {
for prob_vec in prob_map.values() {
let sum: f32 = prob_vec.iter().sum();
assert!((sum - 1.0).abs() < 1e-5);
assert!(prob_vec.iter().all(|&p| p >= 0.0 && p <= 1.0));
}
}
}
#[test]
fn test_darts_current_epoch() {
let device = Device::cuda(0).unwrap_or(Device::default());
let mut darts = DARTS::default(&device).unwrap();
assert_eq!(darts.current_epoch(), 0);
darts.step(0.5, 0.6, None, None).unwrap();
assert_eq!(darts.current_epoch(), 1);
}
}