OK agreed on all points. The apsidal method is described by Marion and Thornton chapter seven of the third edition, and by Fitzgeradl on the university of Texas farside site. I used a combination of both sources.
Note 404(1)
To: Myron Evans <myronevans123>
In eqs. (16-17) the factor m seems to be missing at the LHS due to
f(r) = F(r)/m
but this is not important since the calculation proceeds with f(r) from (21) onwards. I find it a bit audacious to replace a constant (r_c) by a variable (r) in (29) but this seems to be the procedure having done for the apsidal angle calculation. Eq. (26) is obviously taken from the solution of the diff. eq.
x dot dot + omega^2 x = 0
and comparing with (25). It follows that the negative of the expression in parentheses is a frequency. This is a bit difficult to guess for the reader.
Horst