class_docstr: asymmetric negative logistic model of Joe 1990
  
  special case:  a1=a2=1 : symmetric negative logistic of Galambos 1978
  
  restrictions:
   - theta in (0,inf)
   - a1, a2 in (0,1]
code: def evaluate(self, t, a1, a2, theta):
      # if not np.all(self._check_args(a1, a2, theta)):
      #     raise ValueError('invalid args')
  
      a1, a2 = a2, a1
      transf = 1 - (
          (a1 * (1 - t)) ** (-1.0 / theta) + (a2 * t) ** (-1.0 / theta)
      ) ** (-theta)
      return transf
  
imports: import numpy
  from scipy import stats
  from statsmodels.tools.numdiff import _approx_fprime_cs_scalar, approx_hess
label_desc: Use image node_id 2 for calling the AsymNegLogistic obj's underlying member method code with example usage: obj.evaluate(t, a1, a2, theta) and returns: transf