impl<T: Add<Output=T> + Mul<Output=T> + Clone + Zero> SparseVec<T> {

	pub fn zeros(length: usize) -> SparseVec<T> {
		SparseVec {
			length: length,
			data: 	BTreeMap::new()
		}
	}

	pub fn set(&mut self, index: usize, value: T) {
		self.data.insert(index, value);
	}

	pub fn dot(self, rhs: &SparseVec<T>) -> T {
		self.data.into_iter().map(|(k, v)| {
			match rhs.data.get(&k) {
				Some(r) => r.clone() * v,
				None    => Zero::zero()
			}
		}).sum()
	}

	pub fn norm(self) {

	}
}