My question concerns the NP-hardness of the following discrete optimization problem:
Given a matrix $A \in \{ \pm 1 \}^{m\times n}$,
$$\begin{array}{ll} \underset{x \in \{ \pm 1 \}^m ,\, y \in \{ \pm 1 \}^n}{\text{maximize}} & x^T A \, y\end{array}$$
Is this problem known to be NP-hard?