Get learning rate with exponential decay based on current iteration.

        Args:
            iter (int): Current iteration (starting with 0).

        Returns:
            float: Learning rate

def get_learning_rate(self, iter):
        '''
        Get learning rate with exponential decay based on current iteration.

        Args:
            iter (int): Current iteration (starting with 0).

        Returns:
            float: Learning rate
        '''
        lr = self.scheduler.get_learning_rate(iter)
        if iter < self.warmup_iter:
            lr *= (iter + 1) * 1.0 / self.warmup_iter
        return lr