diff --git a/exercise3/wave_1d_parallel.c b/exercise3/wave_1d_parallel.c
index 275a7bf..6857f92 100644
--- a/exercise3/wave_1d_parallel.c
+++ b/exercise3/wave_1d_parallel.c
@@ -74,6 +74,12 @@ void domain_initialize(void) {
   buffers[1] = malloc(bufsize * sizeof(real_t));
   buffers[2] = malloc(bufsize * sizeof(real_t));
 
+  int_t offset = 0;
+  for (int i = 0; i < comm_rank; i++) {
+    int proc_n = N / comm_size + (i < N % comm_size);
+    offset += proc_n;
+  }
+
   for (int_t i = 0; i < n; i++) {
     U_prv(i) = U(i) = cos(2 * M_PI * (i + offset) / (real_t)N);
   }
@@ -125,6 +131,8 @@ void boundary_condition(void) {
 // Communicate the border between processes.
 void border_exchange(void) {
   // BEGIN: T5
+  if (comm_size == 1)
+    return;
   int left = (comm_size + comm_rank - 1) % comm_size;
   int right = (comm_rank + 1) % comm_size;
 
@@ -143,6 +151,8 @@ void border_exchange(void) {
 // to root and assemble it in the root buffer
 void send_data_to_root() {
   // BEGIN: T7
+  if (comm_size == 1)
+    return;
   if (comm_rank != ROOT) {
     MPI_Send(&U(0), n, MPI_DOUBLE, ROOT, 0, MPI_COMM_WORLD);
   } else {
@@ -197,6 +207,7 @@ int main(int argc, char **argv) {
   // BEGIN: T2
   if (comm_rank == ROOT)
     gettimeofday(&t_start, NULL);
+
   simulate();
   MPI_Barrier(MPI_COMM_WORLD);