Writing to a File
Use MPI_File_write or MPI_File_write_at
Use MPI_MODE_WRONLY or MPI_MODE_RDWR as the flags to MPI_File_open
If the file doesn’t exist previously, the flag MPI_MODE_CREATE must also be passed to MPI_File_open
We can pass multiple flags by using bitwise-or ‘|’ in C, or addition ‘+” in Fortran