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//! Sobol initialization
//!
//! Add a Sobol initialization; it should be moved to src-de
/// Generate Sobol quasi-random sequence for initialization
///
/// Uses a simple Sobol sequence implementation for better parameter space coverage
/// than pure random initialization.
///
/// # Arguments
/// * `dimensions` - Number of dimensions (parameters)
/// * `num_samples` - Number of samples to generate
/// * `bounds` - Parameter bounds for scaling
///
/// # Returns
/// Vector of parameter vectors sampled from Sobol sequence
pub fn init_sobol(dimensions: usize, num_samples: usize, bounds: &[(f64, f64)]) -> Vec<Vec<f64>> {
// Simple Sobol implementation - for production use, consider a more sophisticated library
let mut samples = Vec::new();
// Generate quasi-random samples using Van der Corput sequence (simple 1D Sobol)
for i in 0..num_samples {
let mut sample = Vec::with_capacity(dimensions);
for (dim, &(lower, upper)) in bounds.iter().enumerate().take(dimensions) {
// Van der Corput sequence in base 2 for dimension 0, base 3 for dim 1, etc.
let base = match dim {
0 => 2,
1 => 3,
2 => 5,
3 => 7,
4 => 11,
_ => 2 + (dim % 10), // Simple fallback
};
let quasi_random = van_der_corput(i + 1, base);
// Scale to bounds
let scaled = lower + quasi_random * (upper - lower);
sample.push(scaled);
}
samples.push(sample);
}
samples
}
/// Van der Corput sequence for quasi-random number generation
fn van_der_corput(mut n: usize, base: usize) -> f64 {
let mut result = 0.0;
let mut f = 1.0 / base as f64;
while n > 0 {
result += (n % base) as f64 * f;
n /= base;
f /= base as f64;
}
result
}
#[cfg(test)]
mod init_sobol_tests {
use super::*;
#[test]
fn test_van_der_corput() {
// Test basic Van der Corput sequence properties
let val1 = van_der_corput(1, 2);
let val2 = van_der_corput(2, 2);
let val3 = van_der_corput(3, 2);
// Should be in [0, 1)
assert!((0.0..1.0).contains(&val1));
assert!((0.0..1.0).contains(&val2));
assert!((0.0..1.0).contains(&val3));
// Should be different values
assert_ne!(val1, val2);
assert_ne!(val2, val3);
}
#[test]
fn test_init_sobol() {
let bounds = vec![(0.0, 10.0), (0.1, 5.0), (-12.0, 12.0)];
let samples = init_sobol(3, 5, &bounds);
assert_eq!(samples.len(), 5);
for sample in &samples {
assert_eq!(sample.len(), 3);
// Check bounds
assert!((0.0..=10.0).contains(&sample[0]));
assert!((0.1..=5.0).contains(&sample[1]));
assert!((-12.0..=12.0).contains(&sample[2]));
}
}
}