Title: Model agnostic meta-learning on trees. Abstract: In meta-learning, the knowledge learned from previous tasks is transferred to new ones, but this transfer only works if tasks are related, and sharing information between unrelated tasks might hurt performance. A fruitful approach is to share gradients across similar tasks during training, and recent work suggests that the gradients themselves can be used as a measure of task similarity.
We study the case in which datasets associated to different tasks have a hierarchical, tree structure. While a few methods have been proposed for hierarchical meta-learning in the past, we propose the first algorithm that is model-agnostic, a simple extension of MAML. As in MAML, our algorithm adapts the model to each task with a few gradient steps, but the adaptation follows the tree structure: in each step, gradients are pooled across task clusters, and subsequent steps follow down the tree. We test the algorithm on linear and non-linear regression on synthetic data, and show that the algorithm significantly improves over MAML. Interestingly, the algorithm performs best when it does not know in advance the tree structure of the data.