I have a system of ODE with the following peculiar functional structure.

It is second order for one variable, but first order for another one (actually, A and B are some vectors):

```
A'' = f(A, B)
B' = g(A, B)
```

I need the help with the choice of the integrator.

- I can easily convert it to a first-order ODE with the phase space
`(A, A', B)`

and use the corresponding general integrators. - I can also differentiate the second equation once to get a second order ODE and use the corresponding general integrators.

Which approach, do you think, is best? Is there some specialized integrator for this case?