A AugMax Algorithm

The algorithm to generate AugMax images from clean images (i.e., to solve Eq. (4)) is summarized in Algorithm 1, where we employ an accelerated adversarial attack method [28] to reduce complexity. The basic idea behind the acceleration is to early-stop gradient ascend when misclassification has already occurred in k iterations. For all our experiments, we use k = 1, n = 5 and α = 0.1. For AdvMix and AdvMax, we use the worst-of-k method [71] to do adversarial attack on the augmentation hyperparameters such as rotation angles and translation pixel numbers, where k is set to 5. Specifically, for AdvMix, we first randomly select augmentation operations types and mixing parameters as done in AugMix. We then randomly sample k sets of augmentation hyperparameters from the allowed intervals predefined in [5].