code: def _ll_nb2(y, X, beta, alph):
      mu = np.exp(np.dot(X, beta))
      size = 1 / alph
      prob = size / (size + mu)
      ll = nbinom.logpmf(y, size, prob)
      return ll
  
file_path: statsmodels/examples/python/generic_mle.py
imports: import numpy
  from scipy import stats
  import statsmodels.api
  from statsmodels.base.model import GenericLikelihoodModel
  import numpy
  from scipy.stats import nbinom
  from statsmodels.base.model import GenericLikelihoodModel
  import statsmodels.api
label_desc: Use image node_id 1 for calling a global function with example usage: _ll_nb2(y, X, beta, alph) and returns: ll