Solution obtained using an unauthorized or unknown solver

Support
1

I am currently using AMPL to solve a nonlinear equilibrium problem. My AMPL license is the Academic Community Edition, and the nonlinear solver I am using is KNITRO.

According to the AMPL output, the problem appears to be solved successfully; however, when executing the solve command and attempting to retrieve the solution, I encounter the following error message:

Knitro 15.0.1: Locally optimal or satisfactory solution.
objective 20069561.16; feasibility error 3.82e-05
244 iterations; 0 function evaluations

Error at _cmdno 3 executing “solve” command
(file C:\Users\user\AirlineProject\reduce_var_KKT.run, line 18, offset 1801):
Solution obtained using an unauthorized or unknown solver. Please contact support@ampl.com.

Below is the relevant portion of my AMPL code:

reset;
model “C:/Users/user/AirlineProject/GA_relax_KKT.mod”;
data “C:/Users/user/AirlineProject/GA_B&B_6X6_1.dat”;

option solver
“C:/Program Files/Artelys/knitroampl15/knitro-15.0.0-Win64/knitroampl/knitroampl.exe”;

option knitro_options
“bar_feasible=2 nlp_algorithm=1 bar_murule=1
feastol=1e-6 feastol_abs=1e-3
opttol=1e-6 opttol_abs=1e-3”;

solve;

One additional observation is that this error does not occur when I solve smaller test instances; it only appears for larger-scale instances of the same model.

Any guidance or suggestions on how to resolve this issue would be greatly appreciated.

Thank you very much for your time and assistance.

PingHsin

2

Hi @pinghsin

Knitro is not a free solver for Academia, so it’s not included in the Academic Community Edition license. This license is individual and includes all the open-source solvers + 5 commercial solvers: Cplex, Gurobi, Xpress, COPT, and Mosek.

However, if you are teaching optimization, you can apply for AMPL for Courses, a license that includes every solver (such as Knitro) for 6 months. You can share the “AMPL for Courses” license with your students too.