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Hi, I'm trying to fit the lexical decision model in Chapter 7, section 2, and I get an error during inference:

<ipython-input-23-0006ec3856d7>:33: FutureWarning: In v4.0, pm.sample will return an `arviz.InferenceData` object instead of a `MultiTrace` by default. You can pass return_inferencedata=True or return_inferencedata=False to be safe and silence this warning.
  trace = pm.sample(draws=10000, n_init=200000, cores=6, progressbar=True)
Auto-assigning NUTS sampler...
Initializing NUTS using jitter+adapt_diag...
Multiprocess sampling (6 chains in 6 jobs)
NUTS: [threshold, noise, latency_factor, intercept, decay]
<IPython.core.display.HTML object>

C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:224: RuntimeWarning: divide by zero encountered in true_divide
  np.divide(1, self._stds, out=self._inv_stds)
C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:203: RuntimeWarning: invalid value encountered in multiply
  return np.multiply(self._var, x, out=out)
C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:224: RuntimeWarning: divide by zero encountered in true_divide
  np.divide(1, self._stds, out=self._inv_stds)
C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:203: RuntimeWarning: invalid value encountered in multiply
  return np.multiply(self._var, x, out=out)
C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:224: RuntimeWarning: divide by zero encountered in true_divide
  np.divide(1, self._stds, out=self._inv_stds)
C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py:203: RuntimeWarning: invalid value encountered in multiply
  return np.multiply(self._var, x, out=out)
RemoteTraceback: 
"""
Traceback (most recent call last):
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\parallel_sampling.py", line 137, in run
    self._start_loop()
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\parallel_sampling.py", line 191, in _start_loop
    point, stats = self._compute_point()
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\parallel_sampling.py", line 216, in _compute_point
    point, stats = self._step_method.step(self._point)
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\arraystep.py", line 276, in step
    apoint, stats = self.astep(array)
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\base_hmc.py", line 147, in astep
    self.potential.raise_ok(self._logp_dlogp_func._ordering.vmap)
  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py", line 272, in raise_ok
    raise ValueError("\n".join(errmsg))
ValueError: Mass matrix contains zeros on the diagonal. 
The derivative of RV `noise_interval__`.ravel()[0] is zero.
The derivative of RV `intercept_interval__`.ravel()[0] is zero.
"""


The above exception was the direct cause of the following exception:

ValueError: Mass matrix contains zeros on the diagonal. 
The derivative of RV `noise_interval__`.ravel()[0] is zero.
The derivative of RV `intercept_interval__`.ravel()[0] is zero.


The above exception was the direct cause of the following exception:

Traceback (most recent call last):

  File "<ipython-input-23-0006ec3856d7>", line 33, in <module>
    trace = pm.sample(draws=10000, n_init=200000, cores=6, progressbar=True)

  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\sampling.py", line 559, in sample
    trace = _mp_sample(**sample_args, **parallel_args)

  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\sampling.py", line 1477, in _mp_sample
    for draw in sampler:

  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\parallel_sampling.py", line 479, in __iter__
    draw = ProcessAdapter.recv_draw(self._active)

  File "C:\Users\druss\Anaconda3\envs\mypm3env\lib\site-packages\pymc3\parallel_sampling.py", line 359, in recv_draw
    raise error from old_error

RuntimeError: Chain 1 failed.

The only thing I've changed in the code is changing n_jobs to cores, since I'm using a different version of pymc3. Otherwise, I have left your script as is. Also, the first model (the log frequency model) fit just fine.

Have you seen this before? Any idea what the issue is?

Closing this since the issue is resolved by using the SMC sampler.

Correctly me if I wrong - in pyactr-book/book-code/ch7_grodner_gibson/parser_rules.py the purpose of the rule "reanalyse: subject wh" is to revise the initial prediction of subject gapping to a prediction of object gapping. Wouldn't "reanalyse: object wh" be a better name in that case? It confused me when I first saw that rule name. I thought "reanalyse: subject wh" should still predict subject gapping.

Thank you for this. I guess we were thinking about what we were reanalyzing (the initial prediction of subject gap) rather than what we were reanalyzing towards (a non-subject gap). I can't really say which one would be less confusing, but opening this issue here will help either way. Thanks again.

Correctly me if I wrong - in pyactr-book/book-code/ch7_grodner_gibson/parser_rules.py the purpose of the rule "reanalyse: subject wh" is to revise the initial prediction of subject gapping to a prediction of object gapping. Wouldn't "reanalyse: object wh" be a better name in that case? It confused me when I first saw that rule name, because I thought "reanalyse: subject wh" should still predict subject gapping.