Function volatility 

pub fn volatility(returns: &[f64]) -> FinanceResult<f64>

Sample standard deviation of a return series (population divisor n - 1).

Examples

use finance_solution::{volatility, FinanceError};

assert!(volatility(&[0.01, 0.02, -0.01]).is_ok());
match volatility(&[0.01]) {
    Err(FinanceError::Unsolvable { message }) => assert!(message.contains("two")),
    other => panic!("expected Unsolvable, got {other:?}"),
}