Before revision:  We further propose an efficient algorithm, called AdvImmune, which optimizes  meta-gradient in a discrete way to circumvent the computationally expensive combinatorial optimization when solving the adversarial immunization problem.
After revision:  We further propose an effective algorithm, called AdvImmune, which optimizes meta-gradient in a discrete way to circumvent the computationally expensive combinatorial optimization when solving the adversarial immunization problem.