Sampling the Banana-shaped distribution

Sorry to bother you… I’m using Jupyter 4.4.0, Python 3.6.4 on Ubuntu 14.04 and i got this error when running your solution in PyMC3:

BrokenProcessPool: A process in the executor was terminated abruptly while the future was running or pending.

It seems that the problem is in this line:

trace1 = pm.sample(1000, step=pm.NUTS())

I am wondering if there is an easy fix to this … thanks!