methods commonly used for presolving
|SCIP_RETCODE||SCIPshrinkDisjunctiveVarSet (SCIP *scip, SCIP_VAR **vars, SCIP_Real *bounds, SCIP_Bool *boundtypes, SCIP_Bool *redundants, int nvars, int *nredvars, int *nglobalred, SCIP_Bool *setredundant, SCIP_Bool *glbinfeas, SCIP_Bool fullshortening)|
|SCIP_RETCODE SCIPshrinkDisjunctiveVarSet||(||SCIP *||scip,|
try to reduce the necessary variable in a set of variables with corresponding bounds and boundtypes for which one must be fulfilled
e.g. a set of logicor or bounddisjunctive constraint variables would be such a set
consider the following set:
x1 >= 1, x2 >= 3, x3 >= 1, x4 <= 0
by (global) implication data (cliques, implications, and variable bounds) we have also the following implications given:
x1 >= 1 => x3 >= 1 x2 >= 2 => x3 >= 1 x4 <= 0 => x1 >= 1
Because of the last implication x4 is redundant, because x1 >= 1 would also be fulfilled in the variable set, so we can reduce the set by x4. Also, the both other implications and x3 >= 1 (in the given variable set) all imply exactly x3 >= 1, so we tighten the global lower bound of x3 to 1 and the set of variables gets redundant.
scip SCIP data structure vars variables array for which at least one must be fulfilled in the following bounds and boundtypes bounds bounds array for which at least one must be fulfilled boundtypes boundtypes array (TRUE == SCIP_BOUNDTYPE_UPPER, FALSE == SCIP_BOUNDTYPE_LOWER) for which at least one must be fulfilled redundants array which be filled and then indicate if a variable in the set is redundant nvars number of variables nredvars pointer to store how many variables can be removed nglobalred pointer to store number of global reductions on variable bounds found through this set of variables setredundant pointer to store if we found a global reduction on a variable which was part of the given set of variables, this makes this disjunction redundant glbinfeas pointer to store if global infeasibility was detected fullshortening do we want to try the shortening procedure over the whole set (which might be expensive)
References BMSclearMemoryArray, Scip::branchcand, CLEARRATIO, Scip::cliquetable, collectBinaryCliqueData(), collectNonBinaryImplicationData(), collectNonBinaryVBoundData(), Scip::eventqueue, FALSE, Scip::lp, Scip::mem, SCIP_Tree::npendingbdchgs, NULL, Scip::origprob, SCIP_Mem::probmem, Scip::reopt, SCIP_Tree::root, SCIP_Bool, SCIP_BOUNDTYPE_LOWER, SCIP_BOUNDTYPE_UPPER, SCIP_CALL, SCIP_INVALID, SCIP_OKAY, SCIP_Real, SCIP_VARTYPE_BINARY, SCIPallocBufferArray, SCIPallocCleanBufferArray, SCIPcleanupCliques(), SCIPdebugMsg, SCIPfreeBufferArray, SCIPfreeCleanBufferArray, SCIPisGT(), SCIPisLT(), SCIPnodeAddBoundchg(), SCIPprobGetName(), SCIPprobGetNImplBinVars(), SCIPprobGetNVars(), SCIPprobGetVars(), SCIPvarGetLbGlobal(), SCIPvarGetName(), SCIPvarGetProbindex(), SCIPvarGetType(), SCIPvarGetUbGlobal(), SCIPvarIsBinary(), Scip::set, Scip::stat, Scip::transprob, Scip::tree, TRUE, and w.