Monochromatic Bi-Clustering

We propose a natural cost function for the bi-clustering task, the monochromatic cost. This cost function is suitable for detecting meaningful homogeneous bi-clusters based on categorical valued input matrices. Such tasks arise in many applications, such as the analysis of social networks and in systemsbiology where researchers try to infer functional grouping of biological agents based on their pairwise interactions. We analyze the computational complexity of the resulting optimization problem. We present a polynomial time approximation algorithm for this bi-clustering task and complement this result by showing that finding (exact) optimal solutions is NP-hard. As far as we know, these are the first positive approximation guarantees and formal NP-hardness results for any bi-clustering optimization problem. In addition, we show that our optimization problem can be efficiently solved by deterministic annealing, yielding a promising heuristic for large problem instances.