The easiest way to calculate THETA is by using the formula(posted 8816 days ago)THETA = dX(t)/dC(t0) = [ dTHETA/dx0 dTHETA/dg ] [ dTHETAdot/dx0 dTHETAdot/dg ]
where
THETA = THETA0 * cos(kt) + THETAdot0 * sin(kt)/k THETAdot = -THETA0*k*sin(kt) + THETAdot0 * cos(kt)