ValueError: Not enough samples to build a trace

Questions
13

Yes for Windows. After setting cores=1 (which I’d hope I wouldn’t have to when placing the code in a class and using the __main__ clause), I get:

Traceback (most recent call last):
  File "C:/Users/abreucbr/Projects/Scratch/WeibullAFTBayesianFitter.py", line 338, in <module>
    trace = pm.sample(target_accept=0.9, cores=1, init="adapt_diag", draws=draws, tune=tune, random_seed=123,
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\sampling.py", line 586, in sample
    trace = _sample_many(**sample_args)
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\sampling.py", line 700, in _sample_many
    trace = _sample(
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\sampling.py", line 846, in _sample
    for it, (strace, diverging) in enumerate(sampling):
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\fastprogress\fastprogress.py", line 47, in __iter__
    raise e
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\fastprogress\fastprogress.py", line 41, in __iter__
    for i,o in enumerate(self.gen):
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\sampling.py", line 1003, in _iter_sample
    point, stats = step.step(point)
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\step_methods\arraystep.py", line 263, in step
    apoint, stats = self.astep(array)
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\step_methods\hmc\base_hmc.py", line 154, in astep
    self.potential.raise_ok(self._logp_dlogp_func._ordering.vmap)
  File "C:\Users\abreucbr\Miniconda3\lib\site-packages\pymc3\step_methods\hmc\quadpotential.py", line 263, in raise_ok
    raise ValueError('\n'.join(errmsg))
ValueError: Mass matrix contains zeros on the diagonal. 
The derivative of RV `eta`.ravel()[0] is zero.
The derivative of RV `eta`.ravel()[1] is zero.
The derivative of RV `eta`.ravel()[2] is zero.