You simply need to compute the difference between the two vectors:
P1=[ 0.85 4.87]
P2=[ 0.88 4.88]
D = P2 - P1;
quiver( P1(1), P1(2), D(1), D(2), 0 )
The zero as the last argument to quiver tell is to not do automatic scaling. That way you see the arrow actually going between the two points.
