Network pruning is widely used for reducing the heavy computational cost of deep models. A typical pruning algorithm is a three-stage pipeline, i.e., training (a large model), pruning and fine-tuning. During pruning, according to a certain criterion, redundant weights are pruned and important weights are kept to best preserve the accuracy. In this work, we make several surprising observations which contradict common beliefs. For all the six state-of-the-art pruning algorithms we examined, fine-tuning a pruned model only gives comparable or even worse performance than training that model with randomly initialized weights. For pruning algorithms which assume a predefined target network architecture, one can get rid of the full pipeline and directly train the target network from scratch. Our observations are consistent for a wide variety of pruning algorithms with multiple network architectures, datasets, and tasks. Our results have several implications: 1) training a large, over-parameterized model is not necessary to obtain an efficient final model, 2) learned "important" weights of the large model are not necessarily useful for the small pruned model, 3) the pruned architecture itself, rather than a set of inherited "important" weights, is what leads to the efficiency benefit in the final model, which suggests that some pruning algorithms could be seen as performing network architecture search.

本研究发现，在针对低资源设置中减少深度模型推理成本的网络修剪过程中，训练大模型通常不是获得高效终端模型的必要条件，学到的“重要”权重通常对小模型没有用，修剪的架构本身比继承的“重要”权重更重要，并且此方法可作为架构搜索范式。本文还比较了“Lottery Ticket Hypothesis”，发现在最佳学习率下，与随机初始化相比，其“获胜券”初始化并未带来提高。

重新思考网络剪枝的价值