task 3

exercise4/wave_2d_parallel.c

@@ -39,6 +39,13 @@ int world_size;
 int world_rank;
 
 #define ROOT 0
+
+int local_M, local_N;
+
+MPI_Comm cartesian_comm;
+int coordinates[2], dims[2] = { 0 };
+int cartesian_rank;
+
 // END: T1b
 
 // Simulation parameters: size, step count, and how often to save the state
@@ -256,16 +263,46 @@ int main(int argc, char **argv) {
   // TASK: T3
   // Distribute the user arguments to all the processes
   // BEGIN: T3
-  OPTIONS *options = parse_args(argc, argv);
-  if (!options) {
-    fprintf(stderr, "Argument parsing failed\n");
-    exit(EXIT_FAILURE);
+  // create options type for easy broadcast
+  MPI_Datatype options_type;
+  MPI_Type_contiguous(4, MPI_INT64_T, &options_type);
+  MPI_Type_commit(&options_type);
+
+  OPTIONS options;
+  if (world_rank == ROOT) {
+    OPTIONS *parsed = parse_args(argc, argv);
+    if (!parsed) {
+      fprintf(stderr, "Argument parsing failed\n");
+      exit(EXIT_FAILURE);
+    }
+    options = *parsed;
+    free(parsed);
   }
 
-  M = options->M;
-  N = options->N;
-  max_iteration = options->max_iteration;
-  snapshot_freq = options->snapshot_frequency;
+  MPI_Bcast(&options, 1, options_type, ROOT, MPI_COMM_WORLD);
+  MPI_Type_free(&options_type);
+
+  // read options
+  M = options.M;
+  N = options.N;
+  max_iteration = options.max_iteration;
+  snapshot_freq = options.snapshot_frequency;
+
+  // grid dimensions
+  MPI_Dims_create(world_size, 2, dims);
+
+  local_M = M / dims[0];
+  local_N = N / dims[1];
+
+  // create cartesian communicator
+  int periodicity[2] = { 0, 0 };
+  MPI_Cart_create(MPI_COMM_WORLD, 2, dims, periodicity, 1, &cartesian_comm);
+
+  // fetch cartesian coords
+  MPI_Comm_rank(cartesian_comm, &cartesian_rank);
+  MPI_Cart_coords(cartesian_comm, cartesian_rank, 2, coordinates);
+  MPI_Cart_shift(cartesian_comm, 0, 1, &up, &down);
+  MPI_Cart_shift(cartesian_comm, 1, 1, &left, &right);
   // END: T3
 
   // Set up the initial state of the domain
@@ -296,6 +333,7 @@ int main(int argc, char **argv) {
   // TASK: T1d
   // Finalise MPI
   // BEGIN: T1d
+  MPI_Comm_free(&cartesian_comm);
   MPI_Finalize();
   // END: T1d