class_docstr: Relates the variance of a random variable to its mean. Defaults to 1.
  
  Methods
  -------
  call
      Returns an array of ones that is the same shape as `mu`
  
  Notes
  -----
  After a variance function is initialized, its call method can be used.
  
  Alias for VarianceFunction:
  constant = VarianceFunction()
  
  See Also
  --------
  statsmodels.genmod.families.family
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docstr: Derivative of the variance function v'(mu)
docstr_tok: ["Derivative","of","the","variance","function","v","'","(","mu",")"]
code: def deriv(self, mu):
      """
      Derivative of the variance function v'(mu)
      """
      return np.zeros_like(mu)
  
file_path: statsmodels/statsmodels/genmod/families/varfuncs.py
imports: import numpy
label_desc: Use image node_id 2 for calling the VarianceFunction obj's underlying member method code with example usage: obj.deriv(mu) and returns: np