RHS1D:
--------------------------------------------------------------------------
Models a double integrator.
Since version 8.
--------------------------------------------------------------------------
Form:
xDot = RHS1D( x, t, d )
--------------------------------------------------------------------------
------
Inputs
------
x (2,1) State [position;velocity]
t (1,1) Time (not used)
d (1,1)
.a (1,1) Acceleration
-------
Outputs
-------
xDot (3,1) State d[position;velocity;bias]/dt
--------------------------------------------------------------------------
