Function std_dev 

pub fn std_dev(samples: &[f64]) -> f64

Compute sample standard deviation of a slice (Bessel’s correction, n-1).

Returns 0.0 if fewer than 2 elements.

Examples

use batuta_common::math::std_dev;
let data = [2.0, 4.0, 4.0, 4.0, 5.0, 5.0, 7.0, 9.0];
assert!((std_dev(&data) - 2.138).abs() < 0.01);
assert_eq!(std_dev(&[1.0]), 0.0);
assert_eq!(std_dev(&[]), 0.0);