wrap MPI_Cart_sub (#311)

Author: simonbyrne

src/topology.jl

@@ -56,3 +56,17 @@ function Cart_shift(comm::Comm, direction::Integer, disp::Integer)
                   comm, direction, disp, rank_source, rank_dest)
     Int(rank_source[]), Int(rank_dest[])
 end
+
+function Cart_sub(comm::Comm, remain_dims)
+    comm_sub = Comm()
+    remain_dims = [Cint(dim) for dim in remain_dims]
+    # int MPI_Cart_sub(MPI_Comm comm, const int remain_dims[], MPI_Comm *comm_new)
+    @mpichk ccall((:MPI_Cart_sub, libmpi), Cint,
+                  (MPI_Comm, Ptr{Cint}, Ptr{MPI_Comm}),
+                  comm, remain_dims, comm_sub)
+    if comm_sub.val != MPI_COMM_NULL
+        refcount_inc()
+        finalizer(free, comm_sub)
+    end
+    comm_sub
+end

test/test_cart_create.jl

@@ -18,5 +18,15 @@ comm_cart = MPI.Cart_create(comm, ndims, cdims, cperiods, reorder)
 comm_cart2 = MPI.Cart_create(comm, dims, periods, reorder)
 @test MPI.Comm_size(comm_cart2) == nnodes
 
+comm_sub1 = MPI.Cart_sub(comm_cart, (false, true, true))
+@test MPI.Comm_size(comm_sub1) == div(nnodes, dims[1])
+
+comm_sub2 = MPI.Cart_sub(comm_cart, (true, false, true))
+@test MPI.Comm_size(comm_sub2) == div(nnodes, dims[2])
+
+comm_sub3 = MPI.Cart_sub(comm_cart, (true, true, false))
+@test MPI.Comm_size(comm_sub2) == div(nnodes, dims[3])
+
+
 MPI.Finalize()
 #@test MPI.Finalized()