+
+ /* virial - plus sign, as dist_ij = - dist_ji - (really??) */
+ ai->virial.xx+=force.x*dist_ij->x;
+ ai->virial.yy+=force.y*dist_ij->y;
+ ai->virial.zz+=force.z*dist_ij->z;
+ ai->virial.xy+=force.x*dist_ij->y;
+ ai->virial.xz+=force.x*dist_ij->z;
+ ai->virial.yz+=force.y*dist_ij->z;
+