Is it possible to perform backward integration in Simulink, for instance by setting the start time to t_end, the end time to t_start and setting a negative time step (-dt)? Or should I rather try an implementation in Matlab? I need a fixed-step integration scheme.
I need this for a control problem with the application of Pontryagin's principle. For example, see the Section 4 of https://asco.lcsr.jhu.edu/docs/EN530_603_F2015/lecture9.pdf.
Time cannot run backwards in Simulink. You'd need to derive/implement your model using a change of variable where that variable runs forwards.