/* Objective function */
min: 4 x11 + 3 x12 + 2 x13 + 3 x21 + 4 x22 + 5 x23 + 4 x31 + 5 x32 + 6 x33;

/* Variable bounds */

       x11 +   x12 +   x13                                                  = 3;
                               x21 +   x22 +   x23                          = 4;
                                                       x31 +   x32 +   x33  = 5;
       x11                  +  x21                  +  x31                  = 5;
               x12                  +  x22                  +  x32          = 4;
                       x13                  +  x23                  +  x33  = 3;