Solving Constraint Integer Programs

Main problem data

The problem data is accessible in all plugins. The function SCIPgetProbData() returns the pointer to that structure. We use this data structure to store all the information of the binpacking problem. Since this structure is not visible in the other plugins, we implemented setter and getter functions to access this data. The problem data structure SCIP_ProbData is shown below.

** @brief Problem data which is accessible in all places
* This problem data is used to store the input of the binpacking instance, all variables which are created, and all
* constraints.
struct SCIP_ProbData
SCIP_VAR** vars; **< all exiting variables in the problem *
SCIP_CONS** conss; **< set partitioning constraints for each item exactly one *
SCIP_Longint* weights; **< array of item weights *
int* ids; **< array of item ids *
int nvars; **< number of generated variables *
int varssize; **< size of the variable array *
int nitems; **< number of items *
SCIP_Longint capacity; **< bin capacity *

The function SCIPprobdataCreate(), which is called in the reader plugin after the input file was parsed, initializes the problem data structure and creates the problem in the SCIP environment. For this, it creates for each item of the binpacking problem one set covering constraint and creates an initial set of variables for the packings. Note that the set covering constraints have to have the modifiable-flag set to TRUE. This is necessary to tell the solver that these constraints are not completed yet. This means, during the search new variables/packings might be added. The solver needs this information because certain reductions are not allowed. See the body of the function SCIPprobdataCreate() for more details.

A list of all interface methods can be found in probdata_binpacking.h.