- Procedure GMP::Instance::SetCallbackAddLazyConstraint(GMP, callback)
GMP::Instance::SetCallbackAddLazyConstraint
The procedure GMP::Instance::SetCallbackAddLazyConstraint
installs a
callback procedure for adding lazy constraints during the solution
process of a MIP model.
GMP::Instance::SetCallbackAddLazyConstraint(
GMP, ! (input) a generated mathematical program
callback ! (input) an AIMMS procedure
)
Arguments
- GMP
An element in
AllGeneratedMathematicalPrograms
.- callback
A reference to a procedure in the set
AllIdentifiers
.
Return Value
The procedure returns 1 on success, or 0 otherwise.
Note
The callback procedure is called by the solver in these situations
when the solver compares an integer-feasible solution (including an integer-feasible solution provided by a MIP start before any nodes exist) to lazy constraints;
when the LP at a node is unbounded, and a lazy constraint might cut off the primal ray.
The procedure
GMP::SolverSession::GenerateCut
can be used inside aCallbackAddLazyConstraint
callback procedure to add (globally or locally valid) lazy constraints during the MIP branch-and-cut process. Lazy constraints added to the problem are first put into a pool of lazy constraints, so they are not present in the subproblem LP until after the callback is finished.If lazy constraints have been added, the subproblem is re-solved and evaluated, and, if the LP solution is still integer feasible and not cut off, the lazy constraint callback is called again.
The callback procedure should have exactly one argument; a scalar input element parameter into the set
AllSolverSessions
.The
CallbackAddLazyConstraint
callback procedure should have a return value of0, if you want the solution process to stop, or
1, if you want the solution process to continue.
To remove the callback the empty element should be used as the callback argument.
A
CallbackAddLazyConstraint
callback procedure will only be called when solving mixed integer programs with CPLEX or Gurobi.This procedure can also be used for MIQP and MIQCP problems.