PetscSF Object: sf 3 MPI processes
  type: basic
  [0] Number of roots=103, leaves=1, remote ranks=1
  [0] 400 <- (0,101)
  [1] Number of roots=201, leaves=1, remote ranks=1
  [1] 500 <- (0,102)
  [2] Number of roots=301, leaves=2, remote ranks=2
  [2] 600 <- (0,101)
  [2] 601 <- (2,300)
  MultiSF sort=rank-order