_euclidean_sq(vec1, vec2) -> reduce(vec1 - vec2, _a + _*_, 0);
_euclidean(vec1, vec2) -> sqrt(reduce(vec1 - vec2, _a + _*_, 0));
_manhattan(vec1, vec2) -> reduce(vec1-vec2,_a+abs(_),0);
_vec_length(vec) -> sqrt(reduce(vec, _a + _*_, 0));
_round(num,precision) -> round(num/precision)*precision;