Efficient Ising Model Mapping to Solving Slot Placement Problem

Ising model-based computation has attracted attention as it can obtain better solutions of various combinatorial optimization problems at high speed by mapping the problems to natural phenomena. A slot placement problem is one of the combinatorial optimization problems which plays an important role in the optimal logic-block placement as well as optimal delivery decisions but it is known as an NP-hard problem. Solving it efficiently is one of the largest challenges. In this paper, we propose an efficient Ising model mapping to solve the slot placement problem and an interpretation method for the obtained Ising solutions to satisfy the slot-placement constraints. First, we propose slot-placement constraint terms that minimize the energy function or Hamiltonian of the Ising model when satisfying the slot-placement constraints. Secondly, we propose an objective function term in the energy function that minimizes the total weighted wiring length between items to be placed to the slots. In Ising model-based computations, the final spin states cannot necessarily satisfy the slot-placement constraints, which gives one of the largest differences from the conventional computations. Hence we newly propose an interpretation method for the obtained Ising solutions to satisfy the slot-placement constraints. On a fully-connected annealing machine, we could obtain feasible solutions with almost the same accuracy as the simulated annealing for slot placement problem with two orders of magnitude faster.