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Moments: Refactor merge to be in-place

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This commit is contained in:
Vinzent Steinberg 2018-01-11 19:30:51 +01:00
parent 383c85c470
commit 785e2141e0
1 changed files with 9 additions and 16 deletions
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25
src/moments/mod.rs
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@ -150,30 +150,25 @@ impl Moments {
impl Merge for Moments {
#[inline]
fn merge(&mut self, other: &Moments) {
let mut result = Moments::new();
result.n = self.n + other.n;
if result.n == 0 {
return;
}
for i in 0..result.m.len() {
result.m[i] = self.m[i] + other.m[i];
}
let n = f64::approx_from(result.n).unwrap();
let n_a = f64::approx_from(self.n).unwrap();
let n_b = f64::approx_from(other.n).unwrap();
let delta = other.avg - self.avg;
self.n += other.n;
let n = f64::approx_from(self.n).unwrap();
let n_a_over_n = n_a / n;
let n_b_over_n = n_b / n;
let delta = other.avg - self.avg;
result.avg = self.avg + n_b_over_n * delta;
self.avg += n_b_over_n * delta;
let factor_a = -n_b_over_n * delta;
let factor_b = n_a_over_n * delta;
let mut term_a = n_a * factor_a;
let mut term_b = n_b * factor_b;
let prev_m = self.m;
for p in 2..=MAX_P {
term_a *= factor_a;
term_b *= factor_b;
result.m[p - 2] += term_a + term_b;
self.m[p - 2] += other.m[p - 2] + term_a + term_b;
let mut coeff_a = 1.;
let mut coeff_b = 1.;
@ -184,13 +179,11 @@ impl Merge for Moments {
coeff_a *= -n_b_over_n;
coeff_b *= n_a_over_n;
coeff_delta *= delta;
result.m[p - 2] += f64::approx_from(binom.next().unwrap()).unwrap() *
self.m[p - 2] += f64::approx_from(binom.next().unwrap()).unwrap() *
coeff_delta *
(self.m[p - 2 - k] * coeff_a + other.m[p - 2 - k] * coeff_b);
(prev_m[p - 2 - k] * coeff_a + other.m[p - 2 - k] * coeff_b);
}
}
*self = result;
}
}