Attributes

The primary mechanism for querying and modifying properties of a Gurobi model is through the attribute interface. A variety of different attributes are available. Some are only populated at certain times (e.g., those related to the solution of a model), while others are available at all times (e.g., the number of variables in the model). Attributes can be associated with variables (e.g., lower bounds), constraints (e.g., the right-hand side), SOSs (e.g., IIS membership), or with the model as a whole (e.g., the objective value for the current solution).

The following tables list the full set of Gurobi attributes. The attributes have been grouped by associated modeling object. Attributes associated with the model take scalar values. So do attributes associated with solution quality, objectives in multi-objective models, scenarios in multi-scenario models, and batches. Attributes associated with variables, linear constraints, SOS constraints, quadratic constraints, and general constraints contain one entry per variable or constraint in the model. The APIs provide methods to query attribute values for individual constraints or variables, or to query their values for arrays of constraints or variables (refer to our Attribute Examples section for examples). Array queries are generally more efficient.

Note that the attributes that provide solution quality information have been split off into a separate table at the end of this section. These attributes are also associated with the model as a whole.

Some solution attributes require information that is only computed by certain Gurobi algorithms. Such cases are noted in the detailed attribute descriptions that follow. For example, the VBasis and CBasis attributes can only be queried when a simplex basis is available (a basis is available when a continuous model has been solved using primal simplex, dual simplex, or barrier with crossover). Sensitivity information (SAObjLow, SAObjUp, etc.) is also only available for basic solutions.

Model attributes:

These attributes provide information about the overall model (as opposed to information about individual variables or constraints in the model).

Attribute name	Description
NumVars	Number of variables
NumConstrs	Number of linear constraints
NumSOS	Number of SOS constraints
NumQConstrs	Number of quadratic constraints
NumGenConstrs	Number of general constraints
NumNZs	Number of non-zero coefficients in the constraint matrix
DNumNZs	Number of non-zero coefficients in the constraint matrix (in double format)
NumQNZs	Number of non-zero quadratic objective terms
NumQCNZs	Number of non-zero terms in quadratic constraints
NumIntVars	Number of integer variables
NumBinVars	Number of binary variables
NumPWLObjVars	Number of variables with piecewise-linear objective functions
ModelName	Model name
ModelSense	Model sense (minimization or maximization)
ObjCon	Constant offset for objective function
Fingerprint	Model fingerprint
ObjVal	Objective value for current solution
ObjBound	Best available objective bound (lower bound for minimization, upper bound for maximization)
ObjBoundC	Best available objective bound, without rounding (lower bound for minimization, upper bound for maximization)
PoolObjBound	Bound on best objective for solutions not in pool (lower bound for minimization, upper bound for maximization)
PoolObjVal	Objective value of alternatives solutions stored during the optimization process
MIPGap	Current relative MIP optimality gap
Runtime	Runtime for most recent optimization
Work	Work spent on most recent optimization
Status	Current optimization status
SolCount	Number of stored solutions
IterCount	Number of simplex iterations performed in most recent optimization
BarIterCount	Number of barrier iterations performed in most recent optimization
NodeCount	Number of branch-and-cut nodes explored in most recent optimization
OpenNodeCount	Number of open branch-and-cut nodes at the end of most recent optimization
ConcurrentWinMethod	Winning method of most recent concurrent optimization of continuous model
IsMIP	Indicates whether the model is a MIP
IsQP	Indicates whether the model is a QP/MIQP
IsQCP	Indicates whether the model is a QCP/MIQCP
IsMultiObj	Indicates whether the model has multiple objectives
IISMinimal	Indicates whether the current IIS is minimal
MaxCoeff	Maximum constraint matrix coefficient (in absolute value)
MinCoeff	Minimum (non-zero) constraint matrix coefficient (in absolute value)
MaxBound	Maximum finite variable bound
MinBound	Minimum finite variable bound
MaxObjCoeff	Maximum linear objective coefficient (in absolute value)
MinObjCoeff	Minimum (non-zero) linear objective coefficient (in absolute value)
MaxRHS	Maximum constraint right-hand side (in absolute value)
MinRHS	Minimum (non-zero) constraint right-hand side (in absolute value)
MaxQCCoeff	Maximum quadratic constraint matrix coefficient of quadratic part (in absolute value)
MinQCCoeff	Minimum (non-zero) quadratic constraint matrix coefficient of quadratic part (in absolute value)
MaxQCLCoeff	Maximum quadratic constraint matrix coefficient in linear part (in absolute value)
MinQCLCoeff	Minimum (non-zero) quadratic constraint matrix coefficient in linear part (in absolute value)
MaxQCRHS	Maximum quadratic constraint right-hand side (in absolute value)
MinQCRHS	Minimum (non-zero) quadratic constraint right-hand side (in absolute value)
MaxQObjCoeff	Maximum quadratic objective coefficient (in absolute value)
MinQObjCoeff	Minimum (non-zero) quadratic objective coefficient (in absolute value)
Kappa	Estimated basis condition number
KappaExact	Exact basis condition number
FarkasProof	Magnitude of infeasibility violation in Farkas infeasibility proof
TuneResultCount	Number of improved parameter sets found by tuning tool
NumStart	Number of MIP starts
LicenseExpiration	License expiration date

Variable attributes:

These attributes provide information that is associated with specific variables.

Attribute name	Description
LB	Lower bound
UB	Upper bound
Obj	Linear objective coefficient
VType	Variable type (continuous, binary, integer, etc.)
VarName	Variable name
VTag	Variable tag
X	Value in the current solution
Xn	Value in a sub-optimal MIP solution
RC	Reduced cost
BarX	Value in the best barrier iterate (before crossover)
Start	MIP start value (for constructing an initial MIP solution)
VarHintVal	MIP hint value
VarHintPri	MIP hint priority
BranchPriority	Branching priority
Partition	Variable partition
VBasis	Basis status
PStart	Simplex start vector
IISLB	Indicates whether the lower bound participates in the IIS
IISUB	Indicates whether the upper bound participates in the IIS
IISLBForce	Forces variable lower bound into (1) or out of (0) the computed IIS
IISUBForce	Forces variable upper bound into (1) or out of (0) the computed IIS
PoolIgnore	Flag variables to ignore when checking whether two solutions are identical
PWLObjCvx	Indicates whether the variable has a convex piecewise-linear objective
SAObjLow	Objective coefficient sensitivity information
SAObjUp	Objective coefficient sensitivity information
SALBLow	Lower bound sensitivity information
SALBUp	Lower bound sensitivity information
SAUBLow	Upper bound sensitivity information
SAUBUp	Upper bound sensitivity information
UnbdRay	Unbounded ray

Linear constraint attributes:

These attributes provide information that is associated with specific linear constraints.

Attribute name	Description
Sense	Constraint sense ('<', '>', or '=')
RHS	Right-hand side value
ConstrName	Constraint name
CTag	Constraint tag
Pi	Dual value (also known as the shadow price)
Slack	Slack in the current solution
CBasis	Basis status
DStart	Simplex start vector
Lazy	Determines whether a constraint is treated as a lazy constraint
IISConstr	Indicates whether the constraint participates in the IIS
IISConstrForce	Forces constraint into (1) or out of (0) the computed IIS
SARHSLow	Right-hand side sensitivity information
SARHSUp	Right-hand side sensitivity information
FarkasDual	Farkas infeasibility proof

SOS attributes:

These attributes provide information that is associated with specific Special-Ordered Set (SOS) constraints.

Attribute name	Description
IISSOS	Indicates whether the SOS constraint participates in the IIS
IISSOSForce	Forces the SOS constraint into (1) or out of (0) the computed IIS

Quadratic constraint attributes:

These attributes provide information that is associated with specific quadratic constraints.

Attribute name	Description
QCSense	Constraint sense ('<', '>', or '=')
QCRHS	Right-hand side
QCName	Quadratic constraint name
QCPi	Dual value
QCSlack	Slack in the current solution
QCTag	Quadratic constraint tag
IISQConstr	Indicates whether the quadratic constraint participates in the IIS
IISQConstrForce	Forces the quadratic constraint into (1) or out of (0) the computed IIS

General constraint attributes:

These attributes provide information that is associated with specific general constraints. Those starting with “Func” are only for function constraints.

Attribute name	Description
FuncPieceError	Error allowed for PWL translation
FuncPieceLength	Piece length for PWL translation
FuncPieceRatio	Controls whether to under- or over-estimate function values in PWL approximation
FuncPieces	Sets strategy for PWL function approximation
FuncNonlinear	Chooses the approximation approach used to handle a function constraint
GenConstrType	Type of general constraint
GenConstrName	General constraint name
IISGenConstr	Indicates whether the general constraint participates in the IIS
IISGenConstrForce	Forces the general constraint into (1) or out of (0) the computed IIS

Solution quality attributes:

Attribute name	Description
MaxVio	Maximum (unscaled) violation
BoundVio	Maximum (unscaled) bound violation
BoundSVio	Maximum (scaled) bound violation
BoundVioIndex	Index of variable with the largest (unscaled) bound violation
BoundSVioIndex	Index of variable with the largest (scaled) bound violation
BoundVioSum	Sum of (unscaled) bound violations
BoundSVioSum	Sum of (scaled) bound violations
ConstrVio	Maximum (unscaled) constraint violation
ConstrSVio	Maximum (scaled) constraint violation
ConstrVioIndex	Index of constraint with the largest (unscaled) violation
ConstrSVioIndex	Index of constraint with the largest (scaled) violation
ConstrVioSum	Sum of (unscaled) constraint violations
ConstrSVioSum	Sum of (scaled) constraint violations
ConstrResidual	Maximum (unscaled) primal constraint error
ConstrSResidual	Maximum (scaled) primal constraint error
ConstrResidualIndex	Index of constraint with the largest (unscaled) primal constraint error
ConstrSResidualIndex	Index of constraint with the largest (scaled) primal constraint error
ConstrResidualSum	Sum of (unscaled) primal constraint errors
ConstrSResidualSum	Sum of (scaled) primal constraint errors
DualVio	Maximum (unscaled) reduced cost violation
DualSVio	Maximum (scaled) reduced cost violation
DualVioIndex	Index of variable with the largest (unscaled) reduced cost violation
DualSVioIndex	Index of variable with the largest (scaled) reduced cost violation
DualVioSum	Sum of (unscaled) reduced cost violations
DualSVioSum	Sum of (scaled) reduced cost violations
DualResidual	Maximum (unscaled) dual constraint error
DualSResidual	Maximum (scaled) dual constraint error
DualResidualIndex	Index of variable with the largest (unscaled) dual constraint error
DualSResidualIndex	Index of variable with the largest (scaled) dual constraint error
DualResidualSum	Sum of (unscaled) dual constraint errors
DualSResidualSum	Sum of (scaled) dual constraint errors
ComplVio	Maximum complementarity violation
ComplVioIndex	Index of variable with the largest complementarity violation
ComplVioSum	Sum of complementarity violations
IntVio	Maximum integrality violation
IntVioIndex	Index of variable with the largest integrality violation
IntVioSum	Sum of integrality violations

Multi-objective attributes:

Attribute name	Description
ObjN	Objectives of multi-objectives
ObjNCon	Constant terms of multi-objectives
ObjNPriority	Priorities of multi-objectives
ObjNWeight	Weights of multi-objectives
ObjNRelTol	Relative tolerances of multi-objectives
ObjNAbsTol	Absolute tolerances of multi-objectives
ObjNVal	Objective value of multi-objectives solutions
ObjNName	Names of multi-objectives
NumObj	Number of multi-objectives

Multi-scenario attributes:

Attribute name	Description
ScenNLB	Lower bound changes of current scenario in multi-scenario model
ScenNUB	Upper bound changes of current scenario in multi-scenario model
ScenNObj	Objective coefficient changes of current scenario in multi-scenario model
ScenNRHS	Right-hand side changes of current scenario in multi-scenario model
ScenNName	Name of current scenario in multi-scenario model
ScenNObjBound	Objective bound of current scenario in multi-scenario model
ScenNObjVal	Objective value for current solution of current scenario in multi-scenario model
ScenNX	Value in the current solution of current scenario in multi-scenario model
NumScenarios	Number of scenarios

Batch attributes:

Attribute name	Description
BatchErrorCode	Last error code received from the Cluster Manager
BatchErrorMessage	Last error message received from the Cluster Manager
BatchID	ID of the remote batch
BatchStatus	Status of the batch