avoid tuncation error through integer division and promote to use "bigint"...

avoid tuncation error through integer division and promote to use "bigint" instead of "int" to avoid overflows for large systems

src/REPLICA/fix_hyper_local.cpp

@@ -44,9 +44,9 @@ enum{IGNORE,WARN,ERROR};
 /* ---------------------------------------------------------------------- */
 
 FixHyperLocal::FixHyperLocal(LAMMPS *lmp, int narg, char **arg) :
-  FixHyper(lmp, narg, arg), old2now(NULL), xold(NULL), tagold(NULL), 
-  bonds(NULL), numbond(NULL), maxstrain(NULL), maxstrain_region(NULL), 
-  maxstrain_bondindex(NULL), biasflag(NULL), boost(NULL), 
+  FixHyper(lmp, narg, arg), old2now(NULL), xold(NULL), tagold(NULL),
+  bonds(NULL), numbond(NULL), maxstrain(NULL), maxstrain_region(NULL),
+  maxstrain_bondindex(NULL), biasflag(NULL), boost(NULL),
   histo(NULL), allhisto(NULL)
 {
   // error checks
@@ -1274,16 +1274,18 @@ double FixHyperLocal::compute_vector(int i)
   if (i == 3) return 1.0*allbonds/atom->natoms;
 
   if (i == 4) {
-    int nlocal = atom->nlocal;
-    int nbonds = 0;   // BIGINT?
+    const int nlocal = atom->nlocal;
+    bigint nbonds = 0;
     for (int j = 0; j < nlocal; j++)
       nbonds += numbond[j];
-    int allbonds;
-    MPI_Allreduce(&nbonds,&allbonds,1,MPI_INT,MPI_SUM,world);
-    int allneigh;   // BIGINT?
-    MPI_Allreduce(&list->ipage->ndatum,&allneigh,1,MPI_INT,MPI_SUM,world);
-    double neighsperatom = allneigh/atom->natoms; 
-    double bondsperatom = 0.5*allbonds/atom->natoms;
+    bigint allbonds;
+    MPI_Allreduce(&nbonds,&allbonds,1,MPI_LMP_BIGINT,MPI_SUM,world);
+    bigint allneigh,thisneigh;
+    thisneigh = list->ipage->ndatum;
+    MPI_Allreduce(&thisneigh,&allneigh,1,MPI_LMP_BIGINT,MPI_SUM,world);
+    const double natoms = atom->natoms;
+    const double neighsperatom = static_cast<double>(allneigh)/natoms;
+    const double bondsperatom = 0.5*static_cast<double>(allbonds)/natoms;
     return neighsperatom * bondsperatom;
   }