Cant display dual variables values when using solvers highs or cbc

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Hi @JM_slat,

Thanks for reporting this issue. We have just fixed HiGHS (version 20230222 has just been released) and CBC should be fixed soon but the issue seems trickier there.

var x1 >= 0;
var x2>=0;
maximize obj : 2* x1 + 3 * x2;
subject to r1: x1+2*x2 <=5;
subject to r2: 2*x1+x2 <=4;

option solver gurobi;
solve;
display r1, r1.dual;

option solver highs;
solve;
display r1, r1.dual;

produces the following output now:

Gurobi 10.0.0: optimal solution; objective 8
2 simplex iterations
r1 = 1.33333
r1.dual = 1.33333

HiGHS 1.4.0: optimal solution; objective 8
0 simplex iterations
0 barrier iterations
absmipgap=8, relmipgap=inf
r1 = 1.33333
r1.dual = 1.33333
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