Fig. 2: Construct Ising model for a 9-city TSP.
From: Energy-efficient superparamagnetic Ising machine and its application to traveling salesman problems
a Coordinates of all 9 cities used in this problem which are the first 9 cities in the dataset Burma14 from TSPLIB. b Ising spin representation for 9-city TSP (81 spins). Rows indicate names of cities and columns indicate the visiting order. Each spin can be 1 (visited) or −1 (not visited) in each iteration. c Color map of the coupling matrix JTSP of 9-city TSP, and the color bar represents an effective energy with the unit of kT. Here, k is the Boltzmann constant and T is the temperature. d Constrained TSP (CTSP) with a fixed vising sequence from city 2 to city 7 or from city 7 to city 2. The arrows represent the visiting sequence. e The Ising spin representation for CTSP with the fixed visiting sequence in d. Arrows represent possible vising sequences. f Color map of the difference of coupling matrix between TSP (JTSP) in a and CTSP (JCTSP) in d. Arrows represent the fixed vising sequences from city 2 to city 7 or from city 7 to 2.
