Rejecting initial value:
Log probability evaluates to log(0), i.e. negative infinity.
Stan can’t start sampling from this initial value.
Initialization between (-2, 2) failed after 100 attempts.
Try specifying initial values, reducing ranges of constrained values, or reparameterizing the model.
 “Error in sampler$call_sampler(args_list[[i]]) : Initialization failed.”
What package is this simulate_data function coming from? It doesn’t look like it is doing what you think it is doing (calling sampling with the "fixed_param" option and setting the parameters equal to the values in data_listFakeCP).
You can use the _rng functions in the generated quantities block.
The generated quantities block doesn’t affect the inference, so I don’t usually think of it as part of the model so much. Generated quantities is for making predictions based on the output of your model.
Edit: That make sense? I’m not sure I said that clearly.