SCIP

SCIP is currently one of the fastest non-commercial solvers for mixed integer programming (MIP) and mixed integer nonlinear programming (MINLP). It is also a framework for constraint integer programming and branch-cut-and-price. It allows for total control of the solution process and the access of detailed information down to the guts of the solver. The framework used by the driver supports automatic reformulation for many expression types; the modeling guide can be found here.

[Read More] [Modeling guide] [Options] [Changes] [Download SCIP]

How to use it

ampl: option solver scip; # change the solver
ampl: option scip_options 'option1=value1 option2=value2'; # specify options
ampl: solve; # solve the problem

Resources

Solver options

Full list of solver options:

More details on solver options: Features guide.

Retrieving solutions

The outcome of the last optimization is stored in the AMPL parameter solve_result_num and the relative message in solve_result.

display solve_result_num, solve_result;

SCIP solve result codes can be obtained by running scip -! or ampl: shell "scip -!";:

          0- 99 solved: optimal for an optimization problem, feasible for a satisfaction problem
        100-199 solved? solution candidate returned but error likely
            150 solved? MP solution check failed (option sol:chk:fail)
        200-299 infeasible
        300-349 unbounded, feasible solution returned
        350-399 unbounded, no feasible solution returned
        400-449 limit, feasible: stopped, e.g., on iterations or Ctrl-C
        450-469 limit, problem is either infeasible or unbounded
        470-499 limit, no solution returned
        500-999 failure, no solution returned
            550 failure: numeric issue, no feasible solution

For general information, see MP result codes guide.

Changelog

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SCIP Options