Get learning rate with cosine 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 cosine decay based on current iteration.

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

        Returns:
            float: Learning rate
        '''
        return self.init_lr * ((math.cos(iter * 1.0 / (self.max_iter) * math.pi) + 1.0) * 0.5)