Correcting a bug in the batch simulator

The batch simulator was crashing whe giving more tasks to the last process

Author: rsachetto

src/main_batch.c

@@ -64,13 +64,19 @@ int main(int argc, char **argv) {
         num_simulations = total_simulations / num_max_proc;
     }
 
-    int last_rank_extra = total_simulations % num_max_proc;
+    //We have to calculate the simulation start offset before adding the rest to the last process
+    simulation_number_start = rank * num_simulations;
 
-    if (rank == num_max_proc - 1) {
-        num_simulations += last_rank_extra;
+    //The last process will have the rest of the simulations
+    int rest = total_simulations % num_max_proc; 
+    if (rest != 0 && rank == num_max_proc - 1) {
+        num_simulations += rest;
     }
 
-    simulation_number_start = rank * num_simulations;
+    if (num_simulations == 0) {
+        MPI_Finalize();
+        return EXIT_SUCCESS;
+    }
 
     struct user_options *options;
     options = new_user_options();
@@ -98,12 +104,7 @@ int main(int argc, char **argv) {
     options->show_gui = false;
 
     MPI_Barrier(MPI_COMM_WORLD);
-
-    if (num_simulations == 0) {
-        MPI_Finalize();
-        return EXIT_SUCCESS;
-    }
-
+   
     for (int s = simulation_number_start; s < simulation_number_start + num_simulations; s++) {
 
         the_grid = new_grid();