class_docstr: requires theta >=1
class_docstr_tok: ["requires","theta",">","=1"]
code: def deriv2_inverse(self, phi, theta):
      th = theta  # shorthand
      d2 = (phi ** (2 / th) + (th - 1) * phi ** (1 / th)) / (
          phi**2 * th**2
      )
      d2 *= np.exp(-(phi ** (1 / th)))
      return d2
  
imports: import warnings
  import numpy
  from scipy.special import expm1, gamma
label_desc: Use image node_id 6 for calling the TransfGumbel obj's underlying member method code with example usage: obj.deriv2_inverse(phi, theta) and returns: d2