code: def deriv(self, mu):
      return 2 * mu - 6 * mu**2 + 4 * mu**3
  
file_path: statsmodels/examples/python/quasibinomial.py
imports: import statsmodels.api
  import numpy
  import pandas
  import matplotlib.pyplot
  from io import StringIO
label_desc: Use image node_id 2 for calling the vf obj's underlying member method code with example usage: obj.deriv(mu) and returns: unknown