So inspired by this thread on the adjoint ODE solver, what are your experiences with the adjoint solver? Or with the BDF solver? BTW, out of curiosity I’ve reimplemented the nonlinear model from section 4 and it looks like this implementation using Stan’s regular rk45 is quite a bit (~30%) faster than the specialized pmx_solve_twocpt_rk45, is this to be expected? Also, don’t you guys have some kind of adaptive (stiff->non-stiff) and parallel (combining draws across chains for cov-estimation) warm-up. How much faster does this make the problem?