addColumn(index, array) {
            if (typeof array === 'undefined') {
                array = index;
                index = this.columns;
            }
            util.checkColumnIndex(this, index, true);
            array = util.checkColumnVector(this, array);
            for (var i = 0; i < this.rows; i++) {
                this[i].splice(index, 0, array[i]);
            }
            this.columns += 1;
            return this;
        }
Adds a column at the given index
@param {number} [index = this.columns] - Column index
@param {Array|Matrix} array - Array or vector
@return {Matrix} this