added tsp.mod

exercises/ex07/tsp.mod

+reset;
+
+set S ordered;
+param n := card {S};
+
+set SS := 1..(2^n - 2); # 1 to number of subtours
+
+set POW {k in SS} := {i in S: (k div 2^(ord(i)-1)) mod 2 = 1}; # subtours
+
+set LINKS := {i in S, j in S: ord(i) < ord(j)};
+
+param cost {LINKS} >= 0;
+
+var x {LINKS} binary;
+
+minimize tot_cost: sum {(i,j) in LINKS} cost[i,j] * x[i,j];
+
+s.t. tour: sum {(i,j) in LINKS} x[i,j] = n;
+
+s.t. subtour_elim {k in SS : 3 <= card{POW[k]} <= n-1}:
+	sum {i in POW[k], j in POW[k]: (i,j) in LINKS} x[i,j] <= card{POW[k]}-1;
+
+data toy.dat;
+#data 10city.dat;
+#data 12city.dat;
+
+#display SS;
+#display POW;
+
+#option solver cplex;
+
+#solve;
+
+#display x;
+