class LongMatrix implements Serializable {

    public void plusEqual(LongMatrix other) {
        Preconditions.checkArgument(other.rowNum == rowNum && other.colNum == colNum,
            "Matrix size not the same! The rowNums are {},{}; the colNums are {},{}.", rowNum, other.rowNum, colNum,
            other.colNum);
        for (int i = 0; i < rowNum; i++) {
            for (int j = 0; j < colNum; j++) {
                matrix[i][j] += other.matrix[i][j];
            }
        }
    }

    public  LongMatrix(long[][] matrix);

}