nonlinear oscillator rkfixed vs AdamsBDF

Hi Eveyone,

A nonlinear differential equation is solved using rkfixed and AdamsBDF in the attached worksheet. As can be seen on the plots, they return entirely different solutions. The stable solution is reached with rkfixed but not with AdamsBDFF within the specified time period. I wonder which function returns the correct answer.

Your advice is highly appreciated.

All at its best,

From Payman.