Prepare the phase for learning

def set_up_phase(self, training_info, model, source):
        """ Prepare the phase for learning """
        # 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