WilsonTheta is a subclass of TransientIntegrator which implements
the Wilson\Theta method. In the Wilson\Theta method, to determine the
velocities, accelerations and displacements at time t + \theta \Delta
t, \theta \ge 1.37, for \U_{t+ \theta \Delta t}
where we use following functions to relate \Ud_{t + \theta
\Delta t} and \Udd_{t + \theta \Delta t} to \U_{t + \theta \Delta
t} and the response quantities at time t:
which results in the following for determining the responses at
t + \theta \Delta t
The response quantities at time t + \Delta t are then
determined using the following
virtual int formTangent(void)