RK4 is indeed trivial to implement. It is also fairly useless for anything but "easy" problems. I have done a lot of useful science with my own tensorflow imple

RK4 is indeed trivial to implement. It is also fairly useless for anything but "easy" problems. I have done a lot of useful science with my own tensorflow implementation of simple integrators like RK4, but for serious research problems I do need much better solvers. Things that are "better" with modern solvers: computational efficiency (appropriate adaptive choice of step size); numerical stability (detecting when things go wrong); higher precision. And other nice improvements like callbacks and root-finding and sensitivity analysis built into the solvers.