# to run: mpirun -np 4 python mpi_example.py
from mpi4py import MPI
import numpy as np
from netCDF4 import Dataset
rank = MPI.COMM_WORLD.rank  # The process ID (integer 0-3 for 4-process run)
nc = Dataset('parallel_test.nc', 'w', parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info(),format='NETCDF4_CLASSIC')
# below should work also - MPI_COMM_WORLD and MPI_INFO_NULL will be used.
#nc = Dataset('parallel_test.nc', 'w', parallel=True)
d = nc.createDimension('dim',4)
v = nc.createVariable('var', np.int, 'dim')
v[rank] = rank
# switch to collective mode, rewrite the data.
v.set_collective(True)
v[rank] = rank
nc.close()
# reopen the file read-only, check the data
nc = Dataset('parallel_test.nc', parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info())
assert rank==nc['var'][rank]
nc.close()
# reopen the file in append mode, modify the data on the last rank.
nc = Dataset('parallel_test.nc', 'a',parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info())
if rank == 3: v[rank] = 2*rank
nc.close()
# reopen the file read-only again, check the data.
# leave out the comm and info kwargs to check that the defaults
# (MPI_COMM_WORLD and MPI_INFO_NULL) work.
nc = Dataset('parallel_test.nc', parallel=True)
if rank == 3:
    assert 2*rank==nc['var'][rank]
else:
    assert rank==nc['var'][rank]
nc.close()

# to run: mpirun -np 4 python mpi_example.py
from mpi4py import MPI
import numpy as np
from netCDF4 import Dataset
rank = MPI.COMM_WORLD.rank  # The process ID (integer 0-3 for 4-process run)
nc = Dataset('parallel_test.nc', 'w', parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info(),format='NETCDF4_CLASSIC')
# below should work also - MPI_COMM_WORLD and MPI_INFO_NULL will be used.
#nc = Dataset('parallel_test.nc', 'w', parallel=True)
d = nc.createDimension('dim',4)
v = nc.createVariable('var', np.int32, 'dim')
v[rank] = rank
# switch to collective mode, rewrite the data.
v.set_collective(True)
v[rank] = rank
nc.close()
# reopen the file read-only, check the data
nc = Dataset('parallel_test.nc', parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info())
assert rank==nc['var'][rank]
nc.close()
# reopen the file in append mode, modify the data on the last rank.
nc = Dataset('parallel_test.nc', 'a',parallel=True, comm=MPI.COMM_WORLD,
        info=MPI.Info())
if rank == 3: v[rank] = 2*rank
nc.close()
# reopen the file read-only again, check the data.
# leave out the comm and info kwargs to check that the defaults
# (MPI_COMM_WORLD and MPI_INFO_NULL) work.
nc = Dataset('parallel_test.nc', parallel=True)
if rank == 3:
    assert 2*rank==nc['var'][rank]
else:
    assert rank==nc['var'][rank]
nc.close()

create 32 bit integer var, not 64 (to allow test with NETCDF4_CLASSIC)