fn col(&self, index: usize) -> Vec<f64> {
        assert!(index < self.col);
        let mut container: Vec<f64> = vec![0f64; self.row];
        for i in 0..self.row {
            container[i] = self[(i, index)];
        }
        container
    }
Extract Column

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

fn main() {
let a = matrix(c!(1,2,3,4), 2, 2, Row);
assert_eq!(a.col(0), c!(1,3));
}
```
src/structure/matrix.rs