I am trying to modify some source code in ADVI.

I know I can use

```
template <bool propto, bool jacobian_adjust_transforms, typename T> T log_prob
```

to calculate log density. I understand I can let the first option propto=false so as to drop all constants.

But when I compare the result of

`log_prob = model_.template log_prob<false, true>`

and

`log_prob_2 = model_.template log_prob<true, true>`

I find the difference between these two is not a constant. The former one is the same as what I will get if I manually calculate the log density plus jacobian.

For instance, I am playing with the comparison in this line:

Do I misunderstand something on the `propto`

option?