@mzagorowska Interestingly, I just looked at this issue. This isn’t an issue/bug in Alpine. Since you have created a quadratic monomial in x[1]*x[1], this automatically gets reformulated as x[1]^2 within Alpine. Once this is a quadratic function, you can use Gurobi as the underlying mip_solver and it runs without any issue. Although not the best, if you still prefer to use an open-source mip_solver, note that Cbc/HiGHS solver does not support quadratic functions. Instead, you will need to use Pavito.jl solver and then use Cbc/HiGHS and Ipopt as the underlying mip_solver and cont_solver, respectively. Similar to the way it is invoked here: Alpine.jl/runtests.jl at 22c44020fe3c56c4e11bafaebf9c86b313da0714 · lanl-ansi/Alpine.jl · GitHub I tested this and it works fine.