“…Several different exact algorithms have been suggested for this problem, including those described in Christofides and Whitlock (1977), Wang (1983), Viswanathan and Bagchi (1988), Vasko (1989), Dowsland et al (1992), Christofides and Hadjiconstantinou (1995) and Hifi and M'Hallah (2005). Approximate algorithms for this problem have also been proposed by Morabito and Arenales (1996), Cung et al (2000), Belov and Scheithauer (2006), Hifi and M'Hallah (2006), Gongalves (2007) and Cui (2008).…”