Model

class pygcgopt.gcg.Model

Main class for interaction with the GCG solver.

addDecomposition(self, PartialDecomposition partialdec)

Adds a user specified decomposition to GCG.

The passed PartialDecomposition can be partial or finnished. A partial decomposition will be completed by GCG using its detector loop. If a finnished decomposition is passed, GCG will skip the detection loop and use the provided decomposition right away.

addDecompositionFromConss(self, master_conss, *block_conss)

Adds a user specified decomposition to GCG based on constraints.

Parameters

• master_conss – An iterable of Constraint objects. Can be the empty list.

• block_conss – Any number of lists. The Constraints from each list will be turned into their own block. (optional)

Returns

The created PartialDecomposition object

Creates a PartialDecomposition object using createDecomposition(). Fixes the master constraints with fixMasterConss() and the block constraints with fixBlockConss(). The decomposition is added with addDecomposition().

addPreexistingPartialDecomposition(self, PartialDecomposition partialdec)

addVar(self, *args, **kwargs)

createDecomposition(self)

Creates a new empty PartialDecomposition.

The created PartialDecomposition object can be used to fix constraints and variables. Afterwards, it can be passed to the model through addPreexistingPartialDecomposition().

See also

• PartialDecomposition.fixConsToMaster()

• PartialDecomposition.fixConssToMaster()

• PartialDecomposition.fixConsToBlock()

• PartialDecomposition.fixConssToBlock()

• PartialDecomposition.fixConsToBlockId()

• PartialDecomposition.fixConssToBlockId()

createPartialDecomposition(self)

detect(self)

Detect the problem.

Can be executed before or after presolving. If executed before presolving, the structure is detected on the original problem and presolving is skiped when solving the problem later.

See also

• presolve()

• optimize()

getDualbound(self)

Retrieve the best dual bound.

This retrieves the same dual bound that GCG reports in the console log. The dual bound is based on the objective value of the optimized linear programming relaxation at the current node.

Note

The dual bound at the root node is not always equal to the solution of the restricted master problem LP relaxation. This can be due to master cuts or abortion of the pricing loop before the restricted master problem is optimal.

Returns

The best dual bound of the current node.

getMasterProb(self)

Provides access to the GCG master problem.

Returns

An instance of scip#Model that represents the master problem.

getMastervars(self, var)

Returns the master variables corresponding to the variable of original problem

Parameters

var – Variable of original problem

Returns

List of master variables

includeDefaultPlugins(self)

Includes all default plug-ins of GCG into SCIP

Called automatically during initialization of the model.

includeDetector(self, Detector detector, detectorname, decchar, desc, freqcallround=1, maxcallround=INT_MAX, mincallround=0, freqcallroundoriginal=1, maxcallroundoriginal=INT_MAX, mincallroundoriginal=0, priority=0, enabled=True, enabledfinishing=False, enabledpostprocessing=False, skip=False, usefulrecall=False)

includes a detector

Parameters

• detector – An object of a subclass of detector#Detector.

• detectorname – name of the detector

For an explanation for all arguments, see DECincludeDetector().

includePricingSolver(self, PricingSolver pricingSolver, solvername, desc, priority=0, heuristicEnabled=False, exactEnabled=False)

listDecompositions(self) → List[PartialDecomposition]

Lists all finnished decompositions found during the detection loop or provided by the user.

listDetectors(self)

Lists all detectors that are currently included

Returns

A list of strings of the detector names

Note

The detectors can be enabled or disabled using the appropriate methods by passing the name.

See also

• setDetectorEnabled()

• setDetectorFinishingEnabled()

• setDetectorPostprocessingEnabled()

listPricingSolvers(self)

optimize(self)

Optimize the problem.

This will transform, presolve and detect the problem if neccessary. Otherwise, GCG will solve the problem directly.

presolve(self)

Presolve the problem.

printStatistics(self)

Print solving statistics of GCG to stdout.

printVersion(self)

Print version, copyright information and compile mode of GCG and SCIP

setDetectorEnabled(self, detector_name, is_enabled=True)

Enables or disables a detector for detecting partial decompositions.

Parameters

• detector_name – The name of the detector.

• is_enabled – Decides weather the detector should be enabled or diabled.

This is a convenience method to access the boolean parameter “detection/detectors/<name>/enabled”.

Note

Disabling a detector using this method is not enough to ensure that it will not run. In addition setDetectorFinishingEnabled() and setDetectorPostProcessingEnabled() have to be used.

Use listDetectors() to obtain a list of all detectors.

setDetectorFinishingEnabled(self, detector_name, is_enabled=True)

Enables or disables a detector for finishing partial decompositions.

Parameters

• detector_name – The name of the detector.

• is_enabled – Decides weather the detector should be enabled or diabled.

This is a convenience method to access the boolean parameter “detection/detectors/<name>/finishingenabled”.

See also

• setDetectorEnabled()

setDetectorPostprocessingEnabled(self, detector_name, is_enabled=True)

Enables or disables a detector for postprocessing partial decompositions.

Parameters

• detector_name – The name of the detector.

• is_enabled – Decides weather the detector should be enabled or diabled.

This is a convenience method to access the boolean parameter “detection/detectors/<name>/postprocessingenabled”.

See also

• setDetectorEnabled()

setGCGSeparating(self, setting)

Sets parameter settings of all separators

Parameters

setting – the parameter settings (SCIP_PARAMSETTING)

setPricingSolverEnabled(self, pricing_solver_name, is_enabled=True)

Enables or disables exact and heuristic solving for the specified pricing solver.

Parameters

• pricing_solver_name – The name of the pricing solver.

• is_enabled – Decides weather the pricing solver should be enabled or diabled.

This is a convenience method to access the boolean parameters “pricingsolver/<name>/exactenabled” and “pricingsolver/<name>/heurenabled”.

Use listPricingSolvers() to obtain a list of all pricing solvers.

setPricingSolverExactEnabled(self, pricing_solver_name, is_enabled=True)

Enables or disables exact solving for the specified pricing solver.

Parameters

• pricing_solver_name – The name of the pricing solver.

• is_enabled – Decides weather the pricing solver should be enabled or diabled.

This is a convenience method to access the boolean parameter “pricingsolver/<name>/exactenabled”.

Use listPricingSolvers() to obtain a list of all pricing solvers.

setPricingSolverHeuristicEnabled(self, pricing_solver_name, is_enabled=True)

Enables or disables heuristic solving for the specified pricing solver.

Parameters

• pricing_solver_name – The name of the pricing solver.

• is_enabled – Decides weather the pricing solver should be enabled or diabled.

This is a convenience method to access the boolean parameter “pricingsolver/<name>/heurenabled”.

Use listPricingSolvers() to obtain a list of all pricing solvers.

writeAllDecomps(self, directory=u'alldecompositions/', extension=u'dec', bool original=True, bool presolved=True, createDirectory=True)

Writes all decompositions to disk

Parameters

• directory – A path to a folder where to store the decomposition files

• extension – Extension without a dot. Decides the output format. Use “dec” to output decomposition files

• createDirectory – Automatically create the directory specified in directory if it does not exist