Preprocess an $N\times N$ matrix $A$ of real numbers and a collection $\mathcal S = \{S_1, S_2, \dots, S_k\}$ of sets of entries ($S_i\subseteq N\times N$) so that given a sequence $B_1, \dots, B_k$ of $N\times N$ matrices of real numbers, we enumerate the entries of $A\times B_i$ that correspond to $S_i$.