SCIP stages

The SCIP object goes through different stages during the solving process, the transitions from one to the next are presented in the following diagram.

More exhaustively, the stages are:

SCIP_STAGE_INIT         =  0,        /**< SCIP data structures are initialized, no problem exists
SCIP_STAGE_PROBLEM      =  1,        /**< the problem is being created and modified
SCIP_STAGE_TRANSFORMING =  2,        /**< the problem is being transformed into solving data space
SCIP_STAGE_TRANSFORMED  =  3,        /**< the problem was transformed into solving data space
SCIP_STAGE_INITPRESOLVE =  4,        /**< presolving is initialized
SCIP_STAGE_PRESOLVING   =  5,        /**< the problem is being presolved
SCIP_STAGE_EXITPRESOLVE =  6,        /**< presolving is exited
SCIP_STAGE_PRESOLVED    =  7,        /**< the problem was presolved
SCIP_STAGE_INITSOLVE    =  8,        /**< the solving process data is being initialized
SCIP_STAGE_SOLVING      =  9,        /**< the problem is being solved
SCIP_STAGE_SOLVED       = 10,        /**< the problem was solved
SCIP_STAGE_EXITSOLVE    = 11,        /**< the solving process data is being freed
SCIP_STAGE_FREETRANS    = 12,        /**< the transformed problem is being freed
SCIP_STAGE_FREE         = 13         /**< SCIP data structures are being freed

Most functions can be called in a subset of the stages, this is then documented, a runtime check is often added and will throw a SCIP_INVALIDCALL if the stage is not allowed.