class_docstr: Computes dual exponential decay [1].
  y = a1 + a2 Exp[-t / a4] + a3 Exp[-t/a5]
      
docstr: generates a cost function instance from datapoints & evaluation points
code: def CostFactory2(self, pts, datapts, nparams):
      """generates a cost function instance from datapoints & evaluation points"""
      F = CF()
      F.addModel(self.ForwardFactory, nparams, self.__name__)
      self.__cost__ = F.getCostFunction(
          evalpts=pts,
          observations=datapts,
          sigma=sqrt(datapts),
          metric=self.__metric__,
      )
      return self.__cost__
  
file_path: mystic/mystic/models/br8.py
imports: from .abstract_model import AbstractModel
  from numpy import array, asarray
  from numpy import sum
  from numpy import exp, sqrt
  from mystic.forward_model import CostFactory
label_desc: Use image node_id 5 for calling the BevingtonDecay obj's underlying member method code with example usage: obj.CostFactory2(pts, datapts, nparams) and returns: self