int *nall = new int[nbody];

  MPI_Allreduce(ncount,nall,nbody,MPI_INT,MPI_SUM,world);

  // remove d*N - d(d+1)/2 dof for each rigid body if more than 2 atoms in igroup

  // in 3d/2d, remove d*N - d(d+1)/2 dof for each rigid body

  // in 3d, remove an additional dof for each diatomic rigid body

  // http://en.wikipedia.org/wiki/Degrees_of_freedom_(engineering)

  // remove an additional dof for each diatomic rigid body in igroup if d=3

  int n = 0;

  if (domain->dimension == 3) {

    for (int ibody = 0; ibody < nbody; ibody++) {

      if (nall[ibody] > 2) n += 3*nall[ibody] - 6;

      else if (nall[ibody] == 2) n++;

      n += 3*nall[ibody] - 6;

      if (nall[ibody] == 2) n++;

    }

  } else if (domain->dimension == 2) {

    for (int ibody = 0; ibody < nbody; ibody++) {

      if (nall[ibody] > 1) n += 2*nall[ibody] - 3;

    }

    for (int ibody = 0; ibody < nbody; ibody++)

      n += 2*nall[ibody] - 3;

  }

  delete [] ncount;