MPI_Cart_sub(3) on Linux

The text 6fbeafdb35d5, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 8 (Jessie) shipped it.

Partitions a communicator into subgroups which form lower-dimensional cartesian subgrids