code: def set_up_phase(self, training_info, model, source):
          
          # To parameter groups handles properly filtering parameters that don't require gradient
          self._optimizer_instance = self.optimizer_factory.instantiate(model)
          self._source = source
  
          self.special_callback = CycleCallback(
              self._optimizer_instance,
              max_lr=self.max_lr, min_lr=self.min_lr, cycles=self.cycles,
              cycle_len=self.cycle_len, cycle_mult=self.cycle_mult, interpolate=self.interpolate,
              init_iter=self.init_iter, init_lr=self.init_lr
          )
  
          return self._optimizer_instance
docs: Prepare the phase for learning