function Q = quaterr(q, p)%	This will compute the difference between two quaternion% vectors, q and p.  %% Q = quaterr(q1, q2)%% Q = 3x1 error matrix% q and p = 4x1q1 = q(1);q2 = q(2);q3 = q(3);q4 = q(4);p1 = p(1);p2 = p(2);p3 = p(3);p4 = p(4);sgn = 2*sign(q1*p1 + p2*p2 + q3*p3 + q4*p4);Q = sgn*[-q1*p2 + q2*p1 + q3*p4 - q4*p3;...      -q1*p3 - q2*p4 + q3*p1 + q4*p2;...      -q1*p4 + q2*p3 - q3*p2 + q4*p1];