param N := 20;

var m{1..N};

param dist{1..N,1..N} integer > 0;

var x{1..N,1..N} binary;

minimize Total:
  sum{ i in 1..N,j in 1..N: i<>j} dist[i,j]* x[i,j];

C1{k in 1..N}: sum{i in 1..N: i <> k} x[i,k] =1;

C2{k in 1..N}: sum{i in 1..N: i <> k} x[k,i] =1;

C3{i in 2..N, j in 2..N: i <> j}: m[i]-m[j]+N*x[i,j]<=N-1;

C4{i in 2..N}: m[i]<=N-1;


data data20.dat;
option solver cplex;
solve;
display Total;
display x;
display m;