Objective :If there are several solutions find that one which uses the minimal
number of assigned values.
If there is no solution minimize the cost function with the following 
coefficients:

             a1 = 1000000
             a2 =   10000
             a3 =     100
             a4 =       1
             b1 =       0
             b2 =       0
             b3 =       0
             b4 =       0