    def update_learning_rate(self, current_iter, warmup_iter=-1):
        """Update learning rate.

        Args:
            current_iter (int): Current iteration.
            warmup_iter (int)： Warmup iter numbers. -1 for no warmup.
                Default： -1.
        """
        if current_iter > 1:
            for scheduler in self.schedulers:
                scheduler.step()
        # set up warm-up learning rate
        if current_iter < warmup_iter:
            # get initial lr for each group
            init_lr_g_l = self._get_init_lr()
            # modify warming-up learning rates
            # currently only support linearly warm up
            warm_up_lr_l = []
            for init_lr_g in init_lr_g_l:
                warm_up_lr_l.append([v / warmup_iter * current_iter for v in init_lr_g])
            # set learning rate
            self._set_lr(warm_up_lr_l)
Update learning rate.

Args:
current_iter (int): Current iteration.
warmup_iter (int)： Warmup iter numbers. -1 for no warmup.
Default： -1.
opensora/models/super_resolution/basicsr/models/base_model.py