swapColumns(column1, column2) {
                util.checkColumnIndex(this, column1);
                util.checkColumnIndex(this, column2);
                for (var i = 0; i < this.rows; i++) {
                    var temp = this.get(i, column1);
                    this.set(i, column1, this.get(i, column2));
                    this.set(i, column2, temp);
                }
                return this;
            }
Swaps two columns
@param {number} column1 - First column index
@param {number} column2 - Second column index
@return {Matrix} this