Algorithm 4 l∞ Attack for a batch of images

$$\begin{array}{cc}\hfill & 1\mathbf{input}:\text{a batch}\text{of}\text{original}\text{images}\{x_0,x_1,\dots ,x_m\},\text{predictor}F,l_{\infty }\text{upper bound}ϵ,\text{number}\hfill \\ \hfill & \mathsf{o}\mathsf{f}\text{iterations}N\hfill \\ \hfill & 2\mathbf{output}:\text{adversarial}\text{perturbation}\Delta x\hfill \\ \hfill & 3t\leftarrow 0,j\leftarrow 0\hfill \\ \hfill & 4\alpha \leftarrow ϵ∕N\hfill \\ \hfill & 5\mathbf{while}j<N:\hfill \\ \hfill & 6t\leftarrow t+\alpha \cdot \text{sign}\left(\sum _{i=0}^m\nabla F(x_i+t)\right)\hfill \\ \hfill & 7j\leftarrow j+1\hfill \\ \hfill & 8\Delta x\leftarrow t\hfill \end{array}$$