I tried to replace the original test_output_init with test_output_init = pm.Normal('test_output_init', mu=0, sigma=1) and then with test_output_init = pt.as_tensor_variable(0.0, dtype='float64') but in both of the cases i received the same error of the orginal post. I dont really care how test_output_init ends up being initialized because its just a procedural value that i need to initialize for the sake of the scan operation but nothing seems to work.