Function det_permutations 

pub fn det_permutations<T>(a: &DSlice<T, 2, Dense>) -> T
where
    T: ComplexFloat + Add<Output = T> + Sub<Output = T> + Mul<Output = T> + Copy + Default,

Computes the determinant of an n×n matrix using the Leibniz formula. Very slow (O(n!)), only for testing / small matrices.