code: function(j) {
              	if (j > this.elements[0].length) { return null; }
              	var col = [], n = this.elements.length;
              	for (var i = 0; i < n; i++) { col.push(this.elements[i][j - 1]); }
              	return $V(col);
                  }
docs: Returns column k of the matrix as a vector