Capsule Networks Need an Improved Routing Algorithm
This work addresses a critical bottleneck for researchers developing capsule networks, highlighting the need for improved routing methods to achieve their promised advantages.
The paper tackled the problem of routing algorithms in capsule networks not performing as expected, often yielding worse results than simple uniform or random baselines, and showed that these algorithms typically polarize link strengths without changing classification outcomes.
In capsule networks, the routing algorithm connects capsules in consecutive layers, enabling the upper-level capsules to learn higher-level concepts by combining the concepts of the lower-level capsules. Capsule networks are known to have a few advantages over conventional neural networks, including robustness to 3D viewpoint changes and generalization capability. However, some studies have reported negative experimental results. Nevertheless, the reason for this phenomenon has not been analyzed yet. We empirically analyzed the effect of five different routing algorithms. The experimental results show that the routing algorithms do not behave as expected and often produce results that are worse than simple baseline algorithms that assign the connection strengths uniformly or randomly. We also show that, in most cases, the routing algorithms do not change the classification result but polarize the link strengths, and the polarization can be extreme when they continue to repeat without stopping. In order to realize the true potential of the capsule network, it is essential to develop an improved routing algorithm.