zjj52868

53.x1(k)=ptr(1,k-1)+c2/st*(ptr(1,k)-ptr(1,k-1));54.y1(k)=ptr(2,k-1)+c2/st*(ptr(2,k)-ptr(2,k-1));55.z1(k)=ptr(3,k-1)+c2/st*(ptr(3,k)-ptr(3,k-1));56.x(k