A fast and robust exact algorithm for face embedding

We present a new matrix formulation of the face hypercube embedding problem that motivates the design of an efficient search strategy to find an encoding that satisfies all faces of minimum length. Increasing dimensions of the Boolean space are explored; for a given dimension constraints are satisfied one at a time. The following features help to reduce the nodes of the solution space that must be explored: candidate cubes instead of candidate codes are generated, cubes yielding symmetric solutions are not generated, a smaller sufficient set of solutions (producing basic sections) is explored, necessary conditions help discard unsuitable candidate cubes, early detection that a partial solution cannot be extended to be a global solution prunes infeasible portions of the search tree. We have implemented a prototype package MINSK based on the previous ideas and run experiments to evaluate it. The experiments show that MINSK is faster and solves more problems than any available algorithm. Moreover, MINSK is a robust algorithm, while most of the proposed alternatives are not. Besides most problems of the complete MCNC benchmark suite, other solved examples include an important set of decoder PLAs coming from the design of microprocessor instruction sets.