I've got a Simulink model, simply a filtered step given as reference onto a control loop with PI control. There are Delays both in the plant as in the measurement feedback. As the simulation results oscillate heavily (wrong) I take ode15s as Solver. The result is good.
Now I add an "abs"-block to the system output, i.e. not inside the loop. The result BEFORE this block still looks good, but different from before. How can this happen, which one is trustworthy?