Problem with Example 01 volcanic field

I got the following error by running node 7/8:

Traceback (most recent call last):
  File "betvh.py", line 238, in calcProb
    pr123, pr4, pr5, pr6, pa, pc, pa_ave, pc_ave = self.calcPost()
  File "betvh.py", line 847, in calcPost
    tmp = np.random.dirichlet((alpha[i],beta[i]), sample).transpose()
  File "mtrand.pyx", line 4767, in mtrand.RandomState.dirichlet
ValueError: alpha <= 0