Fix: bug of divide_mpi_groups (#6120)

Author: Qianruipku

source/module_base/parallel_global.cpp

@@ -405,14 +405,16 @@ void Parallel_Global::divide_mpi_groups(const int& procs,
         exit(1);
     }
 
-    if(rank < extra_procs)
+    if(rank < extra_procs * (procs_in_group + 1))
     {
+        // The first extra_procs groups have procs_in_group + 1 processes.
         procs_in_group++;
         my_group = rank / procs_in_group;
         rank_in_group = rank % procs_in_group;
     }
     else
     {
+        // The remaining groups have procs_in_group processes.
         my_group = (rank - extra_procs) / procs_in_group;
         rank_in_group = (rank - extra_procs) % procs_in_group;
     }

source/module_cell/test/parallel_kpoints_test.sh

@@ -3,11 +3,15 @@
 np=`cat /proc/cpuinfo | grep "cpu cores" | uniq| awk '{print $NF}'`
 echo "nprocs in this machine is $np"
 
-for i in 4;do
+for ((i=3;i<=4;i++));
+do
     if [[ $i -gt $np ]];then
         continue
     fi
     echo "TEST in parallel, nprocs=$i"
     mpirun -np $i ./cell_ParaKpoints
-    break    
+    if [ $? -ne 0 ]; then
+        echo "TEST in parallel, nprocs=$i failed"
+        exit 1
+    fi  
 done