bernasconi go scip ZIMPL ,<2,4>,<3,5>,<4,6>,<5,7>,<6,8>,<7,9>,<8,10>,<9,11>,<10,12>,<11,13>, <12,14>,<13,15>,<14,16>,<15,17>,<16,18>,<17,19>,<18,20> }; set S4 := { 1 .. 20 }; # define weights param C[S3] := <1,3> 8,<2,4> 8,<3,5> 8,<4,6> 8,<5,7> 8,<6,8> 8,<7,9> 8,<8,10> 8,<9,11> 8, <10,12> 8,<11,13> 8,<12,14> 8,<13,15> 8,<14,16> 8,<15,17> 8,<16,18> 8,<17,19> 8,<18,20> 8; param D[S4] := <1> -4,<2> -4,<3> -8,<4> -8,<5> -8,<6> -8,<7> -8,<8> -8,<9> -8, <10> -8,<11> -8,<12> -8,<13> -8,<14> -8,<15> -8,<16> -8,<17> -8,<18> -8, <19> -4,<20> -4; # number of nodes param nodes := 20; # nodes set N := { 1 to nodes }; # variables var x[N] binary; var z implicit integer >= -infinity; # Objective minimize obj: z; # interacting constraint subto interacting_spins: -z + sum in S3 do C[i,j] * x[i] * x[j] + sum in S4 do D[i] * x[i] <= 0; ]]> This is the example BERNASCONI.20.3 in ZIMPL format from POLIP http://polip.zib.de