Approximate Parallel Annealing Ising Machines (APAIMs): Controller and Arithmetic Design
Qichao Tao, Tingting Zhang, Jie Han · 2023
The demand for solving complex combinatorial optimization problems (COPs) in commercial and industrial applications motivates the development of efficient solvers. Ising model-based computers, or Ising machines, have emerged as high-performance solvers. Recently, an approximate parallel annealing Ising machine (APAIM) has been developed for solving constrained COPs such as the traveling salesman problem (TSP). To provide additional detail about the APAIM, this paper presents the designs of its controller and arithmetic units, especially that of the approximate adders in the local field accumulator units (LAUs) required for computing the Hamiltonian in the Ising model. The controller is implemented as a finite state machine and generates an instruction to determine the system operation. To improve hardware efficiency, the so-called lower-part-OR and truncated adder is used for the mantissa addition of floating-point numbers in the LAUs. Although the solution quality is slightly reduced, the use of approximate adders improves the hardware efficiency of a 64-spin APAIM.