The following labels represent host information.
For each host label, client i contributes an array of IMPI_C_NHOSTS[i] values. The array values are ordered; array[0] is the value for the lowest numbered host, array[IMPI_C_NHOSTS[i] - 1] is the value for the highest numbered host, etc.
The clients read back an array of the collated values; the values for the client 0's hosts begin at index 0, the values for client 1's hosts begin at index IMPI_C_NHOSTS[0], etc.