git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@431 f3b2605a-c512-4ea7-a41b-209d697bcdaa

src/group.cpp

@@ -646,6 +646,31 @@ void Group::vcm(int igroup, double masstotal, double *cm)
   cm[2] /= masstotal;
 }
 
+/* ----------------------------------------------------------------------
+   compute the total force on group of atoms
+------------------------------------------------------------------------- */
+
+void Group::fcm(int igroup, double *cm)
+{
+  int groupbit = bitmask[igroup];
+
+  double **f = atom->f;
+  int *mask = atom->mask;
+  int nlocal = atom->nlocal;
+
+  double flocal[3];
+  flocal[0] = flocal[1] = flocal[2] = 0.0;
+
+  for (int i = 0; i < nlocal; i++)
+    if (mask[i] & groupbit) {
+      flocal[0] += f[i][0];
+      flocal[1] += f[i][1];
+      flocal[2] += f[i][2];
+    }
+
+  MPI_Allreduce(flocal,cm,3,MPI_DOUBLE,MPI_SUM,world);
+}
+
 /* ----------------------------------------------------------------------
    compute the radius-of-gyration of group around center-of-mass cm
    must unwrap atoms to compute Rg correctly

src/group.h

@@ -41,6 +41,7 @@ class Group : protected Pointers {
   void bounds(int, double *);              // bounds of atoms in group
   void xcm(int, double, double *);         // center-of-mass coords of group
   void vcm(int, double, double *);         // center-of-mass velocity of group
+  void fcm(int, double *);                 // total force on group
   double gyration(int, double, double *);  // radius-of-gyration of group
   void angmom(int, double *, double *);    // angular momentum of group
   void inertia(int, double *, double [3][3]);     // inertia tensor

src/style.h

@@ -145,6 +145,7 @@ DumpStyle(xyz,DumpXYZ)
 #include "fix_nph.h"
 #include "fix_npt.h"
 #include "fix_nve.h"
+#include "fix_nve_noforce.h"
 #include "fix_nvt.h"
 #include "fix_plane_force.h"
 #include "fix_print.h"
@@ -192,6 +193,7 @@ FixStyle(msd,FixMSD)
 FixStyle(nph,FixNPH)
 FixStyle(npt,FixNPT)
 FixStyle(nve,FixNVE)
+FixStyle(nve,FixNVENoforce)
 FixStyle(nvt,FixNVT)
 FixStyle(orient/fcc,FixOrientFCC)
 FixStyle(print,FixPrint)

src/variable.cpp

@@ -569,7 +569,7 @@ double Variable::evaluate(char *str, Tree *tree)
 
     // customize by adding group function to this list and to if statement
     //   mass(group),charge(group),xcm(group,dim),vcm(group,dim),
-    //   bound(group,xmin),gyration(group)
+    //   fcm(group,dim),bound(group,xmin),gyration(group)
 
     } else if (strcmp(func,"mass") == 0) {
       if (arg2) error->all("Cannot evaluate variable");
@@ -610,6 +610,17 @@ double Variable::evaluate(char *str, Tree *tree)
       else if (strcmp(arg2,"z") == 0) answer = vcm[2];
       else error->all("Cannot evaluate variable");
 
+    } else if (strcmp(func,"fcm") == 0) {
+      if (!arg2) error->all("Cannot evaluate variable");
+      int igroup = group->find(arg1);
+      if (igroup == -1) error->all("Variable group ID does not exist");
+      double fcm[3];
+      group->fcm(igroup,fcm);
+      if (strcmp(arg2,"x") == 0) answer = fcm[0];
+      else if (strcmp(arg2,"y") == 0) answer = fcm[1];
+      else if (strcmp(arg2,"z") == 0) answer = fcm[2];
+      else error->all("Cannot evaluate variable");
+
     } else if (strcmp(func,"bound") == 0) {
       if (!arg2) error->all("Cannot evaluate variable");
       int igroup = group->find(arg1);