  Two-step predictor/corrector methods are provided to solve three classes of
problems that present themselves as systems of ordinary differential equations
(ODEs). In the first class, velocities are given from which displacements are
to be solved. In the second class, velocities and accelerations are given from
which displacements are to be solved. And in the third class, accelerations are
given from which velocities and displacements are to be solved. Two-step
methods are not self starting, so compatible one-step methods are provided to
take that first step with. An algorithm is presented for controlling the step
size so that the local truncation error does not exceed a specified tolerance.
