(Assuming I have not simplified my problem too much to actually benefit from a solution) the model should be something like:
y_est[ t ] = vp * y[t -  ton]
ton doesn’t need to be integer (actually it should be a float!) but it seems I am not able to find a way to make it work. I also tried to pass ton as a float, and then to “find” the index with a value of the time vector closest to ton, but even that solution gave the same result

For the absence of warning/error, it might be because your run an old version of pytorch? I ran the code from the latest nightly build.

Yes, unfortunately I am forced to run v1.1 because of issue with the nvidia cuda diver on my work pc … :\