We construct several variational integrators—integrators based on a discrete variational principle—for systems with Lagrangians
of the form
L =
L
A
+
ε
L
B
, with
e << 1{\varepsilon \ll 1}, where
L
A
describes an integrable system. These integrators exploit that
e << 1{\varepsilon \ll 1} to increase their accuracy by constructing discrete Lagrangians based on the assumption that the integrator trajectory is
close to that of the integrable system. Several of the integrators we present are equivalent to well-known symplectic integrators
for the equivalent perturbed Hamiltonian systems, but their construction and error analysis is significantly simpler in the
variational framework. One novel method we present, involving a weighted time-averaging of the perturbing terms, removes all
errors from the integration at
\fancyscriptO (e){\fancyscript{O} {(\varepsilon)}}. This last method is implicit, and involves evaluating a potentially expensive time-integral, but for some systems and some
error tolerances it can significantly outperform traditional simulation methods.
Keywords N-Body problems - Hamiltonian systems - Numerical methods - Variational integrators - Symplectic integrators
PACS 95.10.Ce - 45.10.Db - 45.20.Jj - 45.50.Pk