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