code: def logpdf(self, x):
          
          if self.transform is not None:
              x = self.transform(x)       
          return (-self.alpha-1)*np.log(x) - (self.beta/float(x))
docs: Log PDF for Inverse Gamma prior
  
          Parameters
          ----------
          x : float
              Latent variable for which the prior is being formed over
  
          Returns
          ----------
          - log(p(x))