The issue is that the output of function "fun" doesn't match the size of the "ang_f" data. This typically happens when the function you are using to fit the data does not return a vector of the same length as the input "ang_f" data you are trying to model. To fix this you will have to modify "fun" to output vector of dimensions that matches dimensions of "ang_f".
It will be helpful to debug if you attach data.
I hope this helps!
