Hello Jean,
Thank you for your continuing contributions
By the way, did you use rkfixed() on purpose. As usual, did you try to use, say, Rkadapt() or any other solver different than rkfixed(). As we mentioned many times - rkfixed() is not the solver of choice anyway.
Regards,
Radovan
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"