Specifically, the boundary conditions may be, for instance, the position and velocity of the center of gravity at the start point, and the velocity of the center of {HEAD ~ gravity} at {TAIL ~ the end point} 
at
Specifically , the boundary conditions may be , for instance , the position and velocity of the center of gravity at the start point , and the velocity of the center of { HEAD ~ gravity } at { TAIL ~ the end point }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL