int operator() (const multi1d<int>& coordinate) const {return coordinate[dir_decay];}
TimeSliceFunc::operator() (const multi1d<int>& coordinate) const { if ((dir_decay<0)||(dir_decay>=Nd)) { return 0 ; } else { return coordinate[dir_decay] ; } }
  int operator() (const multi1d<int>& coordinate)    const {return coordinate[dir_decay];}