1use crate::{Encoding, VecZnx, ZnxInfos};
 2use rug::Float;
 3use rug::float::Round;
 4use rug::ops::{AddAssignRound, DivAssignRound, SubAssignRound};
 5
 6pub trait Stats {
 7    /// Returns the standard devaition of the i-th polynomial.
 8    fn std(&self, col_i: usize, log_base2k: usize) -> f64;
 9}
10
11impl Stats for VecZnx {
12    fn std(&self, col_i: usize, log_base2k: usize) -> f64 {
13        let prec: u32 = (self.size() * log_base2k) as u32;
14        let mut data: Vec<Float> = (0..self.n()).map(|_| Float::with_val(prec, 0)).collect();
15        self.decode_vec_float(col_i, log_base2k, &mut data);
16        // std = sqrt(sum((xi - avg)^2) / n)
17        let mut avg: Float = Float::with_val(prec, 0);
18        data.iter().for_each(|x| {
19            avg.add_assign_round(x, Round::Nearest);
20        });
21        avg.div_assign_round(Float::with_val(prec, data.len()), Round::Nearest);
22        data.iter_mut().for_each(|x| {
23            x.sub_assign_round(&avg, Round::Nearest);
24        });
25        let mut std: Float = Float::with_val(prec, 0);
26        data.iter().for_each(|x| std += x * x);
27        std.div_assign_round(Float::with_val(prec, data.len()), Round::Nearest);
28        std = std.sqrt();
29        std.to_f64()
30    }
31}