code: def _likelihood(self, args):
          
          #generate image and computes likelihood
          kwargs_data = self.update_data(args)
          imageModel = class_creator.create_image_model(kwargs_data, self._kwargs_psf, self._kwargs_numerics, self._kwargs_model)
          logL = imageModel.likelihood_data_given_model(self._kwargs_lens, self._kwargs_source, self._kwargs_lens_light, self._kwargs_else, source_marg=self._source_marg)
          return logL, None
docs: routine to compute X2 given variable parameters for a MCMC/PSO chainF