gsl_odeiv2 steppers and drivers

[Andrei Kramer]

Hello,
 I have a question regarding ODE steppers. I would like to integrate a
stiff system, and obtain output which is fine grained where needed and
has bold time steps where the trajectory is more flat. This is ideal
for plotting the result I think, and gives me some insight into which
step sizes the integrator thought reasonable. 

So, I wanted to try to use the low-level evolve_apply functions (is
that the right way to go about this?). But the really good solvers for
stiff problems require a driver object, which allocates all of the
arguments for the evolve_apply function internally. I don't see any way
to access those objects. So, I don't know how to call the evolve_apply
function at all, other than making those objects a second time
(manually) and hoping that they are similar enough (i.e. that I don't
specify two very different control functions by accident). It just
seems unatural to have the driver internal step/control function and
another (manually made) step/control function. 

Should I... not try to obtain adaptively spaced output and just pick a
fixed time-step for the trajectory? (this is what I'm doing now)

This would probably mean that I won't know which steps the solver made.
Currently I pick a safe (small) step size so that the plotted curves
look smooth enough.

I suspect that I don't fully understand the reasoning behind the odeiv2
interface.

Best,
Andrei Kramer