addRow(index, array) {
            if (array === undefined) {
                array = index;
                index = this.rows;
            }
            util.checkRowIndex(this, index, true);
            array = util.checkRowVector(this, array, true);
            this.splice(index, 0, array);
            this.rows += 1;
            return this;
        }
Adds a row at the given index
@param {number} [index = this.rows] - Row index
@param {Array|Matrix} array - Array or vector
@return {Matrix} this