Learned Fine-Tuner for Incongruous Few-Shot Learning.

Model-agnostic meta-learning (MAML) effectively meta-learns an initialization of model parameters for few-shot learning where all learning problems share the same format of model parameters -- congruous meta-learning. We extend MAML to incongruous meta-learning where different yet related few-shot learning problems may not share any model parameters. In this setup, we propose the use of a Learned Fine Tuner (LFT) to replace hand-designed optimizers (such as SGD) for the task-specific fine-tuning. The meta-learned initialization in MAML is replaced by learned optimizers based on the learning-to-optimize (L2O) framework to meta-learn across incongruous tasks such that models fine-tuned with LFT (even from random initializations) adapt quickly to new tasks. The introduction of LFT within MAML (i) offers the capability to tackle few-shot learning tasks by meta-learning across incongruous yet related problems (e.g., classification over images of different sizes and model architectures), and (ii) can {efficiently} work with first-order and derivative-free few-shot learning problems. Theoretically, we quantify the difference between LFT (for MAML) and L2O. Empirically, we demonstrate the effectiveness of LFT through both synthetic and real problems and a novel application of generating universal adversarial attacks across different image sources in the few-shot learning regime.