论文标题

CITS:连贯的树木搜索算法,用于求解组合优化问题

CITS: Coherent Ising Tree Search Algorithm Towards Solving Combinatorial Optimization Problems

论文作者

Cen, Yunuo, Das, Debasis, Fong, Xuanyao

论文摘要

模拟退火(SA)在古典启发式算法中吸引了更多的关注,因为组合优化问题的解决方案可以自然映射到Ising Hamiltonian的基态。但是,在实际实施中,退火过程不能任意缓慢,因此它可能会偏离预期的固定玻尔兹曼分布并将其陷入本地能源最低限度。为了克服这个问题,本文提出了一种启发式搜索算法,通过将搜索空间从马尔可夫链扩展到基于SA的递归深度限制树,父母和子节点代表当前和未来的旋转状态。在每次迭代中,算法将通过“向前看”探索可行的搜索空间中最佳的近乎最佳解决方案。此外,由连贯的Ising机器(CIM)激发,我们放宽了自旋状态的离散表示,以使用正则化项的连续表示,并利用振荡器的减少动力学来探索所选树节点的周围邻域。我们在代表性的NP问题(最大切割)上测试了我们的算法,以说明与半明确编程(SDP),SA和模拟CIM相比,该算法的有效性。我们的结果表明,在原始的启发式方法和CIM上方,我们的高级树搜索策略能够在更少的时期内提供解决方案,以解决ISING公式化的NP优化问题。

Simulated annealing (SA) attracts more attention among classical heuristic algorithms because the solution of the combinatorial optimization problem can be naturally mapped to the ground state of the Ising Hamiltonian. However, in practical implementation, the annealing process cannot be arbitrarily slow and hence, it may deviate from the expected stationary Boltzmann distribution and become trapped in a local energy minimum. To overcome this problem, this paper proposes a heuristic search algorithm by expanding search space from a Markov chain to a recursive depth limited tree based on SA, where the parent and child nodes represent the current and future spin states. At each iteration, the algorithm will select the best near-optimal solution within the feasible search space by exploring along the tree in the sense of `look ahead'. Furthermore, motivated by coherent Ising machine (CIM), we relax the discrete representation of spin states to continuous representation with a regularization term and utilize the reduced dynamics of the oscillators to explore the surrounding neighborhood of the selected tree nodes. We tested our algorithm on a representative NP-hard problem (MAX-CUT) to illustrate the effectiveness of this algorithm compared to semi-definite programming (SDP), SA, and simulated CIM. Our results show that above the primal heuristics SA and CIM, our high-level tree search strategy is able to provide solutions within fewer epochs for Ising formulated NP-optimization problems.

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