import numpy as N
import mpi4py.MPI as MPI

# transpose a matrix a into b

a = N.empty((100, 100), dtype=float, order='fortran')
b = N.empty((100, 100), dtype=float, order='fortran')
a.flat = N.arange(a.size, dtype=float)

lb, sizeofdouble = MPI.DOUBLE.Get_extent()

# create datatype dor one row
# (vector with 100 double entries and stride 100)
row = MPI.DOUBLE.Create_vector(100, 1, 100)

# create datatype for matrix in row-major order

# (one hundred copies of the row datatype, strided one word
#  apart; the succesive row datatypes are interleaved)
xpose = row.Create_hvector(100, 1, sizeofdouble)
xpose.Commit()

# send matrix in row-major order and receive in column major order
abuf = MPI.Buffer(a, xpose)
bbuf = MPI.Buffer(b, MPI.DOUBLE)
myrank = MPI.COMM_WORLD.Get_rank() 
status = MPI.Status()
MPI.COMM_WORLD.Sendrecv(abuf, myrank, 0, bbuf, myrank, 0, status)

assert N.allclose(a, b.transpose())
assert status.Get_count(xpose) == 1
assert status.Get_count(MPI.DOUBLE) == b.size

## row.Free()
## xpose.Free()