pub fn cor(v1: &Vec<f64>, v2: &Vec<f64>) -> f64 {
    cov(v1, v2) / (v1.sd() * v2.sd())
}
Pearson's correlation coefficient

# Examples
```
#[macro_use]
extern crate peroxide;
use peroxide::fuga::*;

fn main() {
let a = c!(1,2,3);
let b = c!(3,2,1);
assert!(nearly_eq(cor(&a, &b),-1));
}
```
src/statistics/stat.rs