Parameter Name
Number
Type
Interactive Optimizer Name
Value [Symbolic Constants]
IloCplex::AdvInd
1001
int
0 [CPX_OFF] Off
(do not use advanced start information)
1 [CPX_ON] On (use advanced start information)
Default: 1
Description: Advanced start indicator.
An indicator which, if set to 1, uses advanced starting information when optimization is initiated.
IloCplex::AggCutLim
2054
int
Any non-negative integer
Default: 3
Description: Constraint aggregation limit for cut generation.
Limits the number of constraints that can be aggregated for generating flow cover and mixed integer rounding cuts.
IloCplex::AggFill
1002
int
Any non-negative integer
Default: 10
Description: Preprocessing aggregator fill.
Limits variable substitutions by the aggregator. If the net result of a single substitution is more nonzeros than this value, the substitution is not made.
IloCplex::AggInd
1003
int
-1 Automatic (1 for LP, infinite for MIP)
0 Do not use any aggregator
Any positive integer
Default: -1
Description: Preprocessing aggregator application limit.
Invokes the aggregator to use substitution where possible to reduce the number of rows and columns before the problem is solved. If set to a positive value, the aggregator is applied the specified number of times or until no more reductions are possible.
IloCplex::BarAlg
3007
int
0 Default setting
1 Infeasibility-estimate start
2 Infeasibility-constant start
3 Standard barrier
Default: 0
Description: Barrier algorithm.
The default setting 0 uses the "infeasibility - estimate start" algorithm (setting 1) when solving sub-problems in a Mixed Integer
Programming problem, and the standard barrier algorithm (setting 3) in other cases. The standard barrier algorithm is almost always fastest. However, on problems that are primal or dual infeasible (common for Mixed Integer sub-problems), the standard algorithm may not work as well as the alternatives. The two alternative algorithms (settings 1 and 2) may eliminate numerical difficulties related to infeasibility, but are generally slower.
IloCplex::BarColNz
3009
int
0 Dynamically calculated
or, any positive integer
Default: 0
Description: Barrier column nonzeros.
Used in the recognition of dense columns. If columns in the presolved and aggregated problem exist with more entries than this value, such columns are considered dense and are treated specially by the CPLEX Barrier Optimizer to reduce their effect.
If the problem contains fewer than 400 rows, dense column handling is NOT initiated.
CPX_PARAM_BARCROSSALG IloCplex::BarCrossAlg
3018
int
-1 No crossover
0 Automatic
1 Primal crossover
2 Dual crossover
Default: 0
Description: Barrier crossover method.
Determines which, if any, crossover method is performed at the end of a Barrier optimization called via
CPXhybbaropt(). IloCplex::BarDisplay
3010
int
0 No progress information
1 Normal setup and iteration information
2 Diagnostic information
Default: 1
Description: Barrier display information.
Determines the level of barrier progress information to be displayed.
IloCplex::BarEpComp
3002
double
Any positive number 
1e-12
1e-12 Default: 1e-8
Description: Convergence tolerance.
Sets the tolerance on complementarity for convergence. The barrier algorithm terminates with an optimal solution if the relative complementarity is smaller than this value.
IloCplex::BarGrowth
3003
double
1.0 or greater
Default: 1e8
Description: Barrier growth.
Used to detect unbounded optimal faces. At higher values, the barrier algorithm is less likely to conclude that the problem has an unbounded optimal face, but more likely to have numerical difficulties if the problem has an unbounded face.
IloCplex::BarItLim
3012
int
0 No Barrier iterations
or, any positive integer
Default: Large (varies by computer)
Description: Barrier iteration limit.
Sets the number of Barrier iterations before termination. When set to 0, no Barrier iterations occur, but problem "setup" occurs and information about the setup is displayed (such as Cholesky factorization information).
IloCplex::BarMaxCor
3013
int
-1 Automatically determined
0 None
or, any positive integer
Default: -1
Description: Barrier maximum correction limit.
Sets the maximum number of centering corrections done on each iteration. An explicit value greater than 0 may improve the numerical performance of the algorithm at the expense of computation time.
IloCplex::BarObjRng
3004
double
Any positive number
Default: 1e20
Description: Barrier objective range.
Sets the maximum absolute value of the objective function. The barrier algorithm looks at this limit to detect unbounded problems.
IloCplex::BarOOC
3019
int
0 Off
1 On
Default: 0
Description: Out-of-core barrier indicator.
Specifies whether the barrier optimizer should use out-of-core storage (on disk) for the Cholesky factorization. Disk usage is controlled by the parameters CPX_PARAM_WORKMEM and CPX_PARAM_WORKDIR.
IloCplex::BarOrder
3014
int
0 Automatic
1 Approximate minimum degree (AMD)
2 Approximate minimum fill (AMF)
3 Nested dissection (ND)
Default: 0
Description: Barrier ordering algorithm.
Sets the algorithm to be used to permute the rows of the constraint matrix in order to reduce fill in the Cholesky factor.
IloCplex::BarStartAlg
3017
int
1 Dual is 0
2 Estimate dual
3 Average of primal estimate, dual 0
4 Average of primal estimate, estimate dual
Default: 1
Description: Barrier starting point algorithm.
Sets the algorithm to be used to compute the initial starting point for the barrier optimizer.
IloCplex::BarThreads
3016
int
0 Determined by global thread default
>0 upper limit on threads for Parallel Barrier
Default 0
Description: Barrier thread limit.
Determines the maximum number of parallel processes (threads) that will be invoked by the Parallel Barrier optimizer. The default value of
0 means that the limit will be determined by the value of CPX_PARAM_THREADS, the global thread limit parameter. A positive value will override the value found in CPX_PARAM_THREADS. IloCplex::BarVarUp
3006
double
Any number from 1e-3 to 1e20
Default: 1e20
Description: Variable upper limit.
Sets the upper bound for all variables that have infinite upper bounds. This limit is used to prevent difficulties associated with unbounded optimal faces.
IloCplex::BasInterval
1004
int
Any positive integer
Default: 50,000
Description: Basis file saving frequency.
Establishes the number of iterations between simplex basis file writings.
IloCplex::BBInterval
2039
int
0 Best estimate node always selected
or, any positive integer
Default: 7
Description: MIP strategy bbinterval.
When using nodeselect 2, the bbinterval is the interval at which the best bound node, instead of the best estimate node, is selected from the tree. A bbinterval of 0 means to never select the best bound node. A bbinterval of 1 means to always select the best bound node, and is thus equivalent to
nodeselect 1. Higher values of bbinterval mean that the best bound node will be selected less frequently; experience has shown it to be beneficial to occasionally select the best bound node, and therefore the default bbinterval is 7. IloCplex::BndStrenInd
2029
int
-1 Automatically determined
0 Do not apply bound strengthening
1 Apply bound strengthening
Default: -1
Description: Bound strengthening indicator.
Used when solving mixed integer programs. Bound strengthening tightens the bounds on variables, perhaps to the point where the variable can be fixed and thus removed from consideration during branch & cut. This reduction is usually beneficial, but occasionally, due to its iterative nature, takes a long time.
IloCplex::BrDir
2001
int
-1 [CPX_BrDir_Down] Down branch selected first
0 [CPX_BrDir_Auto] Automatically determined
1 [CPX_BrDir_Up] Up branch selected first
Default: 0
Description: MIP branching direction.
Used to decide which branch, the up or the down branch, should be taken first at each node.
IloCplex::BtTol
2002
double
Any number from 0.0 to 1.0
Default: 0.9999
Description: Backtracking tolerance.
Controls how often backtracking is done during the branching process. The decision when to backtrack depends on three values that change during the course of the optimization:
- the objective function value of the best integer feasible solution ("incumbent")
- the best remaining objective function value of any unexplored node ("best node")
- the objective function value of the most recently solved node ("current objective").
If a cutoff tolerance (see
CPX_PARAM_CUTUP and CPX_PARAM_CUTLO) has been set by the user then that value is used as the incumbent until an integer feasible solution is found. The "target gap" is defined to be the absolute value of the difference between the incumbent and the best node, multiplied by this backtracking parameter. CPLEX does not backtrack until the absolute value of the difference between the current objective and the best node is at least as large as the target gap. Low values of this backtracking parameter thus tend to increase the amount of backtracking, which makes the search process more of a pure best-bound search. Higher parameter values tend to decrease backtracking, making the search more of a pure depth-first search. The backtracking value has effect only after an integer feasible solution is found or when a cutoff has been specified. Note that this backtracking value merely permits backtracking but does not force it; CPLEX may choose to continue searching a limb of the tree if it seems a promising candidate for finding an integer feasible solution. IloCplex::Cliques
2003
int
-1 Do not generate clique cuts
0 Automatically determined
1 Generate clique cuts moderately
2 Generate clique cuts aggressively
Default: 0
Description: MIP cliques indicator.
Determines whether or not clique cuts should be generated for the problem. Setting the value to 0, the default, indicates that the attempt to generate cliques should continue only if it seems to be helping.
IloCplex::ClockType
1006
int
1 CPU time
2 Wall clock time (total physical time elapsed)
Default: 1
Description: Computation time reporting.
Determines how computation times are measured.
IloCplex::CoeRedInd
2004
int
0 Do not use coefficient reduction
1 Reduce only to integral coefficients
2 Reduce all potential coefficients
Default: 2
Description: Coefficient reduction setting
Determines how coefficient reduction is used. Coefficient reduction improves the objective value of the initial (and subsequent) LP relaxations solved during branch & cut by reducing the number of non-integral vertices.
IloCplex::ColGrowth
1047
int
Any integer from 0 to 268,435,450
Default: 100
Description: Variable (column) memory growth.
Sets the extra space allocated for subsequent revisions.
IloCplex::ColReadLim
1023
int
Any integer from 0 to 268,435,450
Default: Varies by computer
Description: Variable (column) read limit.
Sets the number of variables that can be read.
IloCplex::Covers
2005
int
-1 Do not generate cover cuts
0 Automatically determined
1 Generate cover cuts moderately
2 Generate cover cuts aggressively
Default: 0
Description: MIP covers indicator.
Determines whether or not cover cuts should be generated for the problem. Setting the value to 0, the default, indicates that the attempt to generate covers should continue only if it seems to be helping.
IloCplex::CraInd
1007
int
LP Primal:
0 Ignore objective coefficients during crash
-1 or 1 Alternate ways of using objective coefficients
LP Dual:
1 Default starting basis
0 or -1 Aggressive starting basis
QP Primal:
-1 Slack basis
0 Ignore Q terms and use LP solver for crash
1 Ignore objective and use LP solver for crash
QP Dual:
-1 Slack basis
0 or 1 Use Q terms for crash
Description: Simplex crash ordering.
Determines how CPLEX orders variables relative to the objective function when selecting an initial basis.
IloCplex::CutLo
2006
double
Any number
Default: -1e+75
Description: Lower cutoff.
When the problem is a maximization problem, the LOWERCUTOFF parameter is used to cut off any nodes that have an objective value below the lower cutoff value. On a continued mixed integer optimization, the larger of these values and the updated cutoff found during optimization are used during the next mixed integer optimization. A too-restrictive value for the LOWERCUTOFF parameter may result in no integer solutions being found.
IloCplex::CutPass
2056
int
-1 None
0 Automatically determined
Positive values give number of passes to perform
Default: 0
Description: Number of cutting plane passes.
Sets the upper limit on the number of passes CPLEX performs when generating cutting planes on a MIP model.
IloCplex::CutsFactor
2033
double
Any non-negative number
Default: 4.0
Description: Row multiplier factor for cuts.
Limits the number of cuts that can be added. The number of rows in the problem with cuts added is limited to CUTSFACTOR times the original number of rows. If the problem is presolved, the original number of rows is that from the presolved problem.
A CUTSFACTOR of 1.0 or less means that no cuts will be generated. Because cuts can be added and removed during the course of optimization, CUTSFACTOR may not correspond directly to the number of cuts seen during the node log or in the summary table at the end of optimization.
IloCplex::CutUp
2007
double
Any number
Default: 1e+75
Description: Upper cutoff.
Cuts off any nodes that have an objective value above the upper cutoff value, when the problem is a minimization problem. When a mixed integer optimization problem is continued, the smaller of these values and the updated cutoff found during optimization are used during the next mixed integer optimization. A too-restrictive value for the UPPERCUTOFF parameter may result in no integer solutions being found.
IloCplex::DataCheck
1056
int
0 [CPX_OFF] Off (do not check)
1 [CPX_ON] On (check)
Default: 0
Description: Data consistency checking indicator.
When set to
CPX_ON, the CPXcopy____(), CPXread____() and CPXchg____() functions perform extensive checking on data in the array arguments, such as checking that indices are within range, that there are no duplicate entries and that values are valid for the type of data or are valid numbers. This is useful for debugging applications. IloCplex::DepInd
1008
int
0 [CPX_OFF] Off (do not use dependency checker)
1 [CPX_ON] On (use dependency checker)
Default: 0
Description: Dependency indicator.
Determines whether to activate the "dependency checker". If on, the dependency checker searches for dependent rows during preprocessing. If off, dependent rows are not identified.
IloCplex::DisjCuts
2053
int
-1 Do not generate disjunctive cuts
0 Automatically determined
1 Generate disjunctive cuts moderately
2 Generate disjunctive cuts aggressively
3 Generate disjunctive cuts very aggressively
Default: 0
Description: MIP disjunctive cuts indicator.
Determines whether or not disjunctive cuts should be generated for the problem. Setting the value to 0, the default, indicates that the attempt to generate disjunctive cuts should continue only if it seems to be helping.
CPX_PARAM_DIVETYPE IloCplex::DiveType 2060
int
0 automatic
1 traditional dive
2 probing dive
Default: 0
Description: MIP dive strategy.
The MIP traversal strategy occasionally performs probing dives, where it looks ahead at both children nodes before deciding which node to choose. The default (automatic) setting chooses when to perform a probing dive, and the other two settings direct CPLEX when to perform probing dives: never or always.
IloCplex::DPriInd
1009
int
0 [CPX_DPriInd_Auto] Determined automatically
1 [CPX_DPriInd_FULL] Standard dual pricing
2 [CPX_DPriInd_STEEP] Steepest-edge pricing
3 [CPX_DPriInd_Full_Steep]
Steepest-edge pricing in slack space
4 [CPX_DPriInd_SteepQStart]
Steepest-edge pricing, unit initial norms
Default: 0
Description: Dual simplex pricing algorithm.
The default pricing (0) usually provides the fastest solution time, but many problems benefit from alternate settings.
IloCplex::EpAGap
2008
double
Any non-negative number
Default: 1e-06
Description: Absolute mipgap tolerance.
Sets an absolute tolerance on the gap between the best integer objective and the objective of the best node remaining. When this difference falls below the value of the ABSMIPGAP parameter, the mixed integer optimization is stopped.
IloCplex::EpGap
2009
double
Any number from 0.0 to 1.0
Default: 1e-04
Description: Relative mipgap tolerance.
Sets a relative tolerance on the gap between the best integer objective and the objective of the best node remaining. When the value
|bestnode-bestinteger|/(le-10+|bestinteger|) falls below the value of the MIPGAP parameter, the mixed integer optimization is stopped. For example, to instruct CPLEX to stop as soon as it has found a feasible integer solution proved to be within five percent of optimal, set the relative mipgap tolerance to.05.
IloCplex::EpInt
2010
double
Any number from 1e-09 to 1.0
Default: 1e-05
Description: Integrality tolerance.
Specifies the amount by which an integer variable can be different from an integer and still be considered feasible.
IloCplex::EpMrk
1013
double
Any number from 0.0001 to 0.99999
Default: 0.01
Description: Markowitz tolerance.
Influences pivot selection during basis factorization. Increasing the Markowitz threshold may improve the numerical properties of the solution.
IloCplex::EpOpt
1014
double
Any number from 1e-9 to 1e-1
Default: 1e-06
Description: Optimality tolerance.
Influences the reduced-cost tolerance for optimality. This parameter governs how closely CPLEX must approach the theoretically optimal solution.
IloCplex::EpPer
1015
double
Any positive number 1e-8
1e-8 Default: 1e-6
Description: Perturbation constant.
Sets the amount by which CPLEX perturbs the upper and lower bounds on the variables when a problem is perturbed. This parameter can be set to a smaller value if the default value creates too large a change in the problem.
IloCplex::EpRHS
1016
double
Any number from 1e-9 to 1e-1
Default: 1e-06
Description: Feasibility tolerance.
The feasibility tolerance specifies the degree to which a problem's basic variables may violate their bounds. FEASIBILITY influences the selection of an optimal basis and can be reset to a higher value when a problem is having difficulty maintaining feasibility during optimization. You may also wish to lower this tolerance after finding an optimal solution if there is any doubt that the solution is truly optimal. If the feasibility tolerance is set too low, CPLEX may falsely conclude that a problem is infeasible. If you encounter reports of infeasibility during Phase II of the optimization, a small adjustment in the feasibility tolerance may improve performance.
IloCplex::FlowCovers
2040
int
-1 Do not generate flow cover cuts
0 Automatically determined
1 Generate flow cover cuts moderately
2 Generate flow cover cuts aggressively
Default: 0
Description: MIP flow cover cuts indicator.
Determines whether or not to generate flow cover cuts for the problem. Setting the value to 0, the default, indicates that the attempt to
generate flow cover cuts should continue only if it seems to be helping.
IloCplex::FlowPaths
2051
int
-1 Do not generate flow path cuts
0 Automatically determined
1 Generate flow path cuts moderately
2 Generate flow path cuts aggressively
Default: 0
Description: MIP flow path cut indicator.
Determines whether or not flow path cuts should be generated for the problem. Setting the value to 0, the default, indicates that the attempt to generate flow path cuts should continue only if it seems to be helping.
IloCplex::FracCand
2048
int
Any positive integer
Default: 200
Description: Candidate limit for generating Gomory fractional cuts.
Limits the number of candidate variables for generating Gomory fractional cuts.
IloCplex::FracCuts
2049
int
-1 Do not generate Gomory fractional cuts
0 Automatically determined
1 Generate Gomory fractional cuts moderately
2 Generate Gomory fractional cuts aggressively
Default: 0
Description: MIP Gomory fractional cuts indicator.
Determines whether or not Gomory fractional cuts should be generated for the problem. Setting the value to 0, the default, indicates that the attempt to generate Gomory fractional cuts should continue only if it seems to be helping.
IloCplex::FracPass
2050
int
0 Automatic
or, any positive integer
Default: 0
Description: Pass limit for generating Gomory fractional cuts.
Limits the number of passes for generating Gomory fractional cuts. At the default setting of 0, CPLEX decides. The parameter is ignored if the Gomory fractional cut parameter,
CPX_PARAM_FRACCUTS, is set to a nonzero value. IloCplex::GUBCovers
2044
int
-1 Do not generate GUB cuts
0 Automatically determined
1 Generate GUB cuts moderately
2 Generate GUB cuts aggressively
Default: 0
Description: MIP GUB cuts indicator.
Determines whether or not to generate GUB cuts for the problem. Setting the value to 0, the default, indicates that the attempt to
generate GUB cuts should continue only if it seems to be helping.
IloCplex::HeurFreq
2031
int
-1 None
0 Automatic
or, any positive integer
Default: 0
Description: MIP heuristic frequency.
Determines how often to apply the periodic heuristic. Setting the value to -1 turns off the periodic heuristic. Setting the value to 0, the default, applies the periodic heuristic at an interval chosen automatically. Setting the value to a positive number applies the heuristic at the requested node interval. For example, setting HEURISTICFREQ to 20 dictates that the heuristic be called at node 0, 20, 40, 60, etc.
IloCplex::IISInd
1018
int
0 Method with minimum computation time
1 Method generating smaller IIS set
Default: 0
Description: IIS algorithm indicator.
Determines the method to be used to identify the IIS set (see the CPLEX User's Manual for a description of the CPLEX Infeasibility Finder). The default method is the faster method, and works best for most problems. However, if the size of the resulting IIS is large, the alternative method may be useful. The resulting IIS is smaller, although more computation time is usually needed.
IloCplex::ImplBd
2041
int
-1 Do not generate implied bound cuts
0 Automatically determined
1 Generate implied bound cuts moderately
2 Generate implied bound cuts aggressively
Default: 0
Description: MIP implied bound cuts indicator.
Determines whether or not to generate implied bound cuts for the problem. Setting the value to 0, the default, indicates that the attempt to generate implied bound cuts should continue only if it seems to be helping.
IloCplex::IntSolLim
2015
int
Any positive integer
Default: Large (varies by computer)
Description: MIP solution limit.
Sets the number of MIP solutions to be found before stopping.
IloCplex::ItLim
1020
int
Any non-negative integer
Default: Large (varies by computer)
Description: Simplex maximum iteration limit.
Sets the maximum number of iterations to be performed before the algorithm terminates without reaching optimality.
IloCplex::RootAlg
1062
int
0
[CPX_ALG_AUTOMATIC] Automatic 1
[CPX_ALG_PRIMAL] Primal Simplex 2
[CPX_ALG_DUAL] Dual Simplex 3
[CPX_ALG_NET] Network Simplex 4
[CPX_ALG_BARRIER] Barrier 5
[CPX_ALG_SIFTING] Sifting 6
[CPX_ALG_CONCURRENT] Concurrent Dual, Barrier and Primal Default: 0
Description: Method for linear optimization.
Determines which algorithm is used when
CPXlpopt() (or "optimize" in the Interactive Optimizer) is invoked. Currently, the behavior of the Automatic setting is that CPLEX almost always invokes the dual simplex method. The one exception is when solving the relaxation of an MILP model when multiple threads have been requested. In this case, the Automatic setting will use the concurrent optimization method. The Automatic setting may be expanded in the future so that CPLEX chooses the method based on additional problem characteristics. IloCplex::MIPDisplay
2012
int
0 No display
1 Display integer feasible solutions
2 Display nodes under CPX_PARAM_MIPInterval
3 Same as 2 with information on node cuts
4 Same as 3 with LP subproblem information at root
5 Same as 4 with LP subproblem information at nodes
Default: 2
Description: MIP node log display information.
Determines what CPLEX reports to the screen during mixed integer optimization. The amount of information displayed increases with increasing values of this parameter. A setting of 0 causes no node log to be displayed until the optimal solution is found. A setting of 1 displays an entry for each integer feasible solution found. Each entry contains the objective function value, the node count, the number of unexplored nodes in the tree, and the current optimality gap. A setting of 2 also generates an entry for every nth node (where n is the setting of the MIP INTERVAL parameter). A setting of 3 additionally generates an entry for every nth node giving the number of cuts added to the problem for the previous INTERVAL nodes. A setting of 4 additionally generates entries for the LP root
relaxation according to the 'SET SIMPLEX DISPLAY' setting. A setting of 5 additionally generates entries for the LP subproblems, also according to the 'SET SIMPLEX DISPLAY' setting.
IloCplex::MIPEmphasis
2058
int
0 [
CPX_MIPEMPHASIS_BALANCED] Balance optimality and feasibility 1 [CPX_MIPEMPHASIS_FEASIBILITY] Emphasize feasibility over optimality
2 [CPX_MIPEMPHASIS_OPTIMALITY] Emphasize optimality over feasibility
3 [
CPX_MIPEMPHASIS_BESTBOUND] Emphasize moving best bound Default: 0
Description: MIP emphasis indicator.
When set to FEASIBILITY, causes CPLEX to generate more feasible solutions as it optimizes the problem.
IloCplex::MIPInterval
2013
int
Any positive integer
Default: 100
Description: MIP node log interval.
Controls the frequency of node logging when
CPX_PARAM_MIPDISPLAY is set higher than 1. IloCplex::MIPOrdInd
2020
int
0 [CPX_OFF] Off (do not use order information)
1 [CPX_ON] On (use order information if it exists)
Default: 1
Description: MIP priority order indicator.
When set to on, uses the priority order (if it exists) for the next mixed integer optimization.
IloCplex::MIPOrdType
2032
int
0 Do not generate a priority order
1 [CPX_MIPOrder_Cost] Use decreasing cost
2 [CPX_MIPOrder_Bounds]
Use increasing bound range
3 [CPX_MIPOrder_ScaledCost]
Use increasing cost per coefficient count
Default: 0
Description: MIP priority order generation.
Used to select the type of generic priority order to generate when no priority order is present.
IloCplex::MIPStart
2035
int
0 [CPX_OFF] Do not use starting values
1 [CPX_ON] Use starting values at node 0
Default: 0
Description: Indicator for starting MIP values.
Used to indicate how the MIP advanced starting values are used. A setting of 1 indicates that the values should be checked to see if they provide an integer feasible solution before starting optimization.
CPX_PARAM_MIPTHREADS IloCplex::MIPThreads 2014
int
0 determined by global thread default
>0 upper limit on threads for Parallel MIP
Default: 0
Description: MIP thread limit
Determines the maximum number of parallel processes (threads) that will be invoked by the Parallel MIP optimizer. The default value of
0 means that the limit will be determined by the value of CPX_PARAM_THREADS, the global thread limit parameter. A positive value will override the value found in CPX_PARAM_THREADS. IloCplex::MIRCuts
2052
int
-1 Do not generate MIR cuts
0 Automatically determined
1 Generate MIR cuts moderately
2 Generate MIR cuts aggressively
Default: 0
Description: MIP MIR (mixed integer rounding) cut indicator.
Determines whether or not to generate MIR cuts for the problem. Setting the value to 0, the default, indicates that the attempt to
generate MIR cuts should continue only if it seems to be helping.
IloCplex::NetDisplay
5005
int
0 [CPXNET_NO_DISPLAY_OBJECTIVE] No display
1 [CPXNET_TRUE_OBJECTIVE]
Display true objective values
2 [CPXNET_PENALIZE_OBJECTIVE]
Display penalized objective values
Default: 2
Description: Network logging display indicator.
Settings 1 and 2 differ only during Phase I. Setting 2 shows monotonic values, whereas 1 usually does not.
IloCplex::NetEpOpt
5002
double
Any number from 1e-11 to 1e-1
Default: 1e-6
Description: Optimality tolerance for
CPXNETprimopt(). The optimality tolerance specifies the amount a reduced cost may violate the criterion for an optimal solution.
IloCplex::NetEpRHS
5003
double
Any number from 1e-11 to 1e-1
Default: 1e-6
Description: Feasibility tolerance for
CPXNETprimopt(). The feasibility tolerance specifies the degree to which a problem's flow value may violate its bounds. This tolerance influences the selection of an optimal basis and can be reset to a higher value when a problem is having difficulty maintaining feasibility during optimization. You may also wish to lower this tolerance after finding an optimal solution if there is any doubt that the solution is truly optimal. If the feasibility tolerance is set too low, CPLEX may falsely conclude that a problem is infeasible. If you encounter reports of infeasibility during Phase II of the optimization, a small adjustment in the feasibility tolerance may improve performance.
IloCplex::NetFind
1022
int
1 [CPX_NETFIND_PURE] Extract pure network only
2 [CPX_NETFIND_REFLECT] Try reflection scaling
3 [CPX_NETFIND_SCALE] Try general scaling
Default: 2
Description: Simplex network extraction level.
IloCplex::NetItLim
5001
int
Any non-negative integer
Default: Large (varies by computer)
Sets the maximum number of iterations to be performed before the algorithm terminates without reaching optimality.
IloCplex::NetPPriInd
5004
int
0 [CPXNET_PRICE_AUTO] Automatic
1 [CPXNET_PRICE_PARTIAL] Partial pricing
2 [CPXNET_PRICE_MULT_PART] Multiple partial pricing
3 [CPXNET_PRICE_SORT_MULT_PART]
Multiple partial pricing with sorting
Default: 0
Description: Network Simplex pricing algorithm.
The default (0) shows best performance for most problems, and currently is equivalent to 3.
IloCplex::NodeFileInd
2016
int
0 No node file
1 Node file in memory and compressed
2 Node file on disk
3 Node file on disk and compressed
Default: 1
Description: Node storage file indicator.
Used when working memory, WORKMEM, has been exceeded by the size of the tree. If the node file parameter is set to zero when the tree memory limit is reached, optimization is terminated. Otherwise, a group of nodes is removed from the in-memory set as needed. By default, CPLEX transfers nodes to node files when the in-memory set is larger than 128 MBytes, and it keeps the resulting node `files' in compressed form in memory. At settings 2 and 3, the node files are transferred to disk, in compressed and uncompressed form respectively, into a directory named by the WORKDIR parameter, and CPLEX actively manages which nodes remain in memory for processing.
The use of node files is described in more detail in the CPLEX User's Manual.
IloCplex::NodeLim
2017
int
Any non-negative integer
Default: Large (varies by computer)
Description: MIP node limit.
Sets the maximum number of nodes solved before the algorithm terminates, without reaching optimality.
IloCplex::NodeSel
2018
int
0 [CPX_NODESEL_DFS] Depth-first search
1 [CPX_NODESEL_BESTBOUND] Best-bound search
2 [CPX_NODESEL_BESTEST] Best-estimate search
3 [CPX_NODESEL_BESTEST_ALT]
Alternative best-estimate search
Default: 1
Description: MIP node selection strategy.
Used to set the rule for selecting the next node to process when backtracking. The depth-first search strategy chooses the most recently created node. The best-bound strategy chooses the node with the best objective function for the associated LP relaxation. The best-estimate strategy selects the node with the best estimate of the integer objective value that would be obtained from a node once all integer infeasibilities are removed. An alternative best-estimate search is also available.
IloCplex::NzGrowth
1048
int
Any integer from 0 to 268,435,450
Default: 500
Description: Nonzero element memory growth.
Sets the growth policy for subsequent revisions.
IloCplex::NzReadLim
1024
int
Any integer from 0 to 268,435,450
Default: Varies by computer
Description: Nonzero element read limit.
Sets the number of nonzeros that can be read.
IloCplex::ObjDif
2019
double
Any number
Default: 0.0
Description: Absolute objective difference cutoff.
Used to update the cutoff each time a mixed integer solution is found. This absolute value is subtracted from (added to) the newly found integer objective value when minimizing (maximizing). This forces the mixed integer optimization to ignore integer solutions that are not at least this amount better than the one found so far. The OBJDIFFERENCE parameter can be adjusted to improve problem solving efficiency by limiting the number of nodes; however, setting this parameter at a value other than zero (the default) can cause some integer solutions, including the true integer optimum, to be missed. Negative values for this parameter can result in some integer solutions that are worse than or the same as those previously generated, but does not necessarily result in the generation of all possible integer solutions.
IloCplex::ObjLLim
1025
double
Any number
Default: -1e+75
Description: Lower objective value limit.
Setting a lower objective function limit causes CPLEX to halt the optimization process once the minimum objective function value limit has been exceeded. This limit applies only during Phase II of the simplex method.
IloCplex::ObjULim
1026
double
Any number
Default: 1e+75
Description: Upper objective value limit.
Setting an upper objective function limit causes CPLEX to halt the optimization process once the maximum objective function value limit has been exceeded. This limit applies only during Phase II of the simplex method.
IloCplex::PerInd
1027
int
0 [CPX_OFF] Off
1 [CPX_ON] On
Default: 0
Description: Simplex perturbation indicator.
Setting this parameter to 1 causes all problems to be automatically perturbed as optimization begins. A setting of 0 allows CPLEX to determine dynamically, during solution, whether progress is slow enough to merit a perturbation. The situations in which a setting of 1 helps are rare and restricted to problems that exhibit extreme degeneracy.
IloCplex::PerLim
1028
int
0 Determined automatically
or, any positive integer
Default: 0
Description: Simplex perturbation limit.
Sets the number of stalled iterations before perturbation is performed.
IloCplex::PPriInd
1029
int
-1 [CPX_PPRIIND_PARTIAL] Reduced-cost pricing
0 [CPX_PPRIIND_AUTO]
Hybrid reduced-cost & devex pricing
1 [CPX_PPRIIND_DEVEX] Devex pricing
2 [CPX_PPRIIND_STEEP] Steepest-edge pricing
3 [CPX_PPRIIND_STEEPQSTART]
Steepest-edge pricing with slack initial norms
4 [CPX_PPRIIND_FULL] Full pricing
Default: 0
Description: Primal Simplex pricing algorithm.
The default pricing (0) usually provides the fastest solution time, but many problems benefit from alternative settings.
IloCplex::PreCompress
1066
int
-1 Off
0 Automatic
1 On
Default: 0
Description: Compression of original model after presolve.
Specifies whether CPLEX should compress the original model after presolve is performed. This can save considerable storage space for large models. Under the automatic setting, CPLEX will decide whether to perform the compression based on model characteristics.
IloCplex::PreDual
1044
int
-1 Off
0 Automatic
1 On
Default: 0
Description: Presolve dual setting.
Determines whether CPLEX Presolve should pass the primal or dual linear programming problem to the linear programming optimization algorithm. By default, CPLEX chooses automatically. If the DUAL indicator is set to 1, the CPLEX presolve algorithm is applied to the primal problem, but the resulting dual linear program is passed to the optimizer. This is a useful technique for problems with more constraints than variables.
IloCplex::PreInd
1030
int
0 [CPX_OFF] Off (do not use presolve)
1 [CPX_ON] On (use presolve)
Default: 1
Description: Presolve indicator.
When set to 1, invokes the CPLEX Presolve to simplify and reduce problems.
1058
int
0 Only linear reductions
1 Full reductions
Default: 1
Description: Linear reduction indicator.
If only linear reductions are performed, each variable in the original model can be expressed as a linear form of variables in the presolved model. This guarantees, for example, that users can add their own custom cuts to the presolved model.
IloCplex::PrePass
1052
int
-1 Determined automatically
0 Do not use Presolve
or, any positive integer
Default: -1
Description: Limit on the number of Presolve passes made.
When set to a nonzero value, invokes the CPLEX Presolve to simplify and reduce problems.
When set to a positive value, the Presolve is applied the specified number of times, or until no more reductions are possible. At the default value of -1, Presolve should continue only if it seems to be helping.
IloCplex::PreslvNd
2037
int
-1 No node presolve
0 Automatic
1 Force node presolve
Default: 0
Description: Node presolve selector.
Indicates whether node presolve should be performed at the nodes of a mixed integer programming solution. Node presolve can significantly reduce solution time for some models. The default setting is generally effective at determining whether to apply node presolve, although runtimes can be reduced for some models by turning node presolve off.
IloCplex::PriceLim
1010
int
0 Determined automatically
or, any positive integer
Default: 0
Description: Simplex pricing candidate list size.
Sets the maximum number of variables kept in the pricing candidate list.
IloCplex::Probe
2042
int
-1 No probing
0 Automatic
1-3 Probing level
Default: 0
Description: MIP probe.
Determines the amount of probing on variables to be performed before MIP branching. Higher settings perform more probing. Probing can be very powerful but very time consuming at the start. Setting the parameter to values above the default of 0 (automatic) can result in dramatic reductions or dramatic increases in solution time, depending on the model.
CPX_PARAM_QPMAKEPSDIND IloCplex::QPmakePSDInd 4010
int
0 [CPX_OFF] Off
1 [CPX_ON] On
Default: On
Description: Indefinite MIQP indicator.
Determines whether CPLEX will attempt to adjust a MIQP formulation, in which all the variables appearing in the quadratic term are binary. When this feature is active, adjustments will be made to the elements of a quadratic matrix that is not nominally positive semi-definite ("PSD", as required by CPLEX for all QP formulations), to make it PSD, and will also attempt to tighten an already PSD matrix for better numerical behavior. The default setting of
1 means "yes" but you can turn it off if necessary; most models should benefit from the default setting. CPX_PARAM_QPMETHOD IloCplex::RootAlg
1063
int
0
[CPX_ALG_AUTOMATIC] Automatic 1
[CPX_ALG_PRIMAL] Primal Simplex 2
[CPX_ALG_DUAL] Dual Simplex 3
[CPX_ALG_NET] Network Simplex 4
[CPX_ALG_BARRIER] Barrier Default: 0
Description: Method for continuous quadratic optimization.
Determines which algorithm is used when
CPXqpopt() (or "optimize" in the Interactive Optimizer) is invoked. Currently, the behavior of the Automatic setting is that CPLEX invokes the barrier method for continuous QP models, and the dual simplex method for root relaxations of MIQP models. The Automatic setting may be expanded in the future so that CPLEX chooses the method based on additional problem characteristics. IloCplex::QPNzGrowth
4002
int
Any integer from 0 to 268,435,450
Default: 200
Description: QP Q matrix memory growth.
Sets the growth policy for subsequent revisions.
IloCplex::QPNzReadLim
4001
int
Any integer from 0 to 268,435,450
Default: 500
Description: QP Q matrix nonzero read limit.
Sets the number of Q matrix nonzeros that can be read.
IloCplex::Reduce
1057
int
0 No primal and dual reductions
1 Only primal reductions
2 Only dual reductions
3 Both primal and dual reductions
Default: 3
Description: Primal and dual reduction type.
Determines whether primal reductions, dual reductions, or both, are performed during preprocessing.
IloCplex::ReInv
1031
int
0 Determined automatically
or, any integer from 1 to 10,000
Default: 0
Description: Simplex refactorization frequency.
Sets the number of iterations between refactorizations of the basis matrix.
IloCplex::RelaxPreInd
2034
int
0 [CPX_OFF] Off
(do not use presolve on initial relaxation)
1 [CPX_ON] On (use presolve on initial relaxation)
Default: 0
Description: Relaxed LP presolve indicator.
Determines whether LP presolve is applied to the root relaxation in a mixed integer program. Sometimes additional reductions can be made beyond any MIP presolve reductions that were already done.
IloCplex::RelObjDif
2022
double
Any number from 0.0 to 1.0
Default: 0.0
Description: Relative objective difference cutoff.
Used to update the cutoff each time a mixed integer solution is found. The value is multiplied by the absolute value of the integer objective and subtracted from (added to) the newly found integer objective when minimizing (maximizing). This forces the mixed integer optimization to ignore integer solutions that are not at least this amount better than the one found so far. The relative objective difference parameter can be adjusted to improve problem solving efficiency by limiting the number of nodes; however, setting this parameter at a value other than zero (the default) can cause some integer solutions, including the true integer optimum, to be missed. If both RELOBJDIFFERENCE and OBJDIFFERENCE are nonzero, the value of OBJDIFFERENCE is used.
IloCplex::ReverseInd
1032
int
0 [CPX_OFF] Off (do not reverse bytes)
1 [CPX_ON] On (reverse bytes)
Default: 0
Description: SAV file reading byte-reverse indicator.
If set to 1, reverses the byte ordering when reading SAV files. This is useful when a SAV file was created on one system, but is to be read on another system which uses a different byte ordering convention (for example, PCs versus many UNIX systems).
IloCplex::RowGrowth
1046
int
Any integer from 0 to 268,435,450
Default: 100
Description: Constraint (row) memory growth.
Sets the growth policy for subsequent revisions.
IloCplex::RowReadLim
1021
int
Any integer from 0 to 268,435,450
Default: Varies by computer
Description: Constraint (row) read limit.
Sets the number of constraints that can be read.
IloCplex::ScaInd
1034
int
-1 No scaling
0 Equilibration scaling method
1 More aggressive scaling
Default: 0
Description: Scale parameter.
Sets the method to be used for scaling the problem matrix.
1035
int
0 [CPX_OFF] Off
1 [CPX_ON] On
Default: 0
Description: Messages to screen indicator.
Indicates whether or not results messages are displayed on screen.
CPX_PARAM_SIFTALG IloCplex::SiftAlg
1077
int
0 Automatic
1 Primal simplex
2 Dual simplex
3 Network simplex
4 Barrier
Default: 0
Description: Sifting subproblem algorithm
Sets the algorithm to be used for solving sifting subproblems.
CPX_PARAM_SIFTDISPLAY IloCplex::SiftDisplay
1076
int
0 No display
1 Display major iterations
2 Display LP subproblem information
within each sifting iteration
Default: 1
Description: Sifting display information.
Determines the amount of sifting progress information to be displayed.
CPX_PARAM_SIFTITLIM IloCplex::SiftItLim
1078
int
Any non-negative integer
Default: Large (varies by computer)
Description: Upper limit on sifting iterations.
Sets the maximum number of sifting iterations that may be performed if convergence to optimality has not been reached.
IloCplex::SimDisplay
1019
int
0 No iteration messages until solution
1 Iteration info after each refactorization
2 Iteration info for each iteration
Default: 1
Description: Simplex iteration display information.
Determines how often CPLEX reports during simplex optimization.
CPX_PARAM_SIMTHREADS IloCplex::SimThreads 1036
int
0 determined by global thread default
>0 upper limit on threads for Parallel Simplex
Default: 0
Description: Simplex thread limit.
Determines the maximum number of parallel processes (threads) that will be invoked by the Parallel Dual Simplex optimizer. The default value of
0 means that the limit will be determined by the value of CPX_PARAM_THREADS, the global thread limit parameter. A positive value will override the value found in CPX_PARAM_THREADS. Parallel Dual Simplex is supported only on certain hardware operating-system combinations. IloCplex::SingLim
1037
int
Any positive integer
Default: 10
Description: Simplex singularity repair limit.
Restricts the number of times CPLEX attempts to repair the basis when singularities are encountered. Once this limit is exceeded, CPLEX replaces the current basis with the best factorizable basis that has been found.
IloCplex::RootAlg
2025
int
0
[CPX_ALG_AUTOMATIC] Automatic 1
[CPX_ALG_PRIMAL] Primal Simplex 2
[CPX_ALG_DUAL] Dual Simplex 3
[CPX_ALG_NET] Network Simplex 4
[CPX_ALG_BARRIER] Barrier 5
[CPX_ALG_SIFTING] Sifting 6
[CPX_ALG_CONCURRENT] Concurrent Dual, Barrier and Primal Default: 0
Description: MIP starting LP algorithm.
Determines which LP algorithm should be used to solve the initial relaxation of the MIP.
IloCplex::StrongCandLim
2045
int
Any positive number
Default: 10
Description: MIP candidate list
Controls the length of the candidate list when using the "strong branching" variable selection setting
('SET MIP STRATEGY VARIABLESELECT 3').
IloCplex::StrongItLim
2046
int
Any positive number
Default: 0
Description: MIP simplex iterations
Controls the number of simplex iterations performed on each variable in the candidate list when using the "strong branching" variable
selection setting ('SET MIP STRATEGY VARIABLESELECT 3'). The default setting 0 chooses the iteration limit automatically.
IloCplex::StrongThreadLim
2047
int
Any positive number
Default: 1
Description: MIP parallel threads
Controls the number of parallel threads used to perform strong branching. Note that this parameter does nothing if the MIP thread limit ('SET MIP LIMITS THREADS') is greater than 1. Note also that the global thread limit, CPX_PARAM_THREADS, does not affect this parameter.
IloCplex::NodeAlg
2026
int
1
[CPX_ALG_PRIMAL] Primal Simplex 2
[CPX_ALG_DUAL] Dual Simplex 3
[CPX_ALG_NET] Network Simplex 4
[CPX_ALG_BARRIER] Barrier 5
[CPX_ALG_SIFTING] Sifting Default: 2
Description: MIP subproblem LP algorithm.
Sets the algorithm to be used on MIP subproblems.
CPX_PARAM_SYMMETRY IloCplex::Symmetry 2059
int
0 [CPX_OFF] Off
1 [CPX_ON] On
Default: Off
Description: Symmetry breaking cuts.
Determines whether symmetry breaking cuts may be added, during the preprocessing phase, to a MIP model.
CPX_PARAM_THREADS IloCplex::Threads 1067
int
Minimum: 1
Maximum: determined by license key and computer
Default: 1
Description: Global default thread count.
Determines the default number of parallel processes (threads) that will be invoked by any CPLEX parallel optimizer. This provides a convenient way to control parallelism with a single parameter setting. The value in place for this parameter can be overridden for any particular CPLEX parallel optimizer by setting the appropriate thread limit (
CPX_PARAM_BARTHREADS, CPX_PARAM_MIPTHREADS, or CPX_PARAM_SIMTHREADS). IloCplex::TiLim
1039
double
Any non-negative number
Default: 1e+75
Description: Global time limit.
Sets the maximum time, in seconds, for computations before termination, as measured according to the setting of the CLOCKTYPE parameter. The time limit applies to primal simplex, dual simplex, barrier, and mixed integer optimizations, as well as infeasibility finder computations. (Network simplex and barrier crossover operations are exceptions; these processes do not terminate if the time limit is exceeded.) The time limit includes preprocessing time. For `hybrid' optimizations (such as network optimization followed by dual or primal simplex, barrier optimization followed by crossover), the cumulative time applies.
IloCplex::TreLim
2027
double
Any non-negative number
Default: 1e+75
Description: Tree memory limit.
Sets an absolute upper limit on the size (in megabytes) of the branch & cut tree. If this limit is exceeded, CPLEX terminates optimization.
IloCplex::VarSel
2028
int
-1 [CPX_VARSEL_MININFEAS]
Branch on variable with minimum infeasibility
0 [CPX_VARSEL_DEFAULT]
Branch variable automatically selected
1 [CPX_VARSEL_MAXINFEAS]
Branch on variable with maximum infeasibility
2 [CPX_VARSEL_PSEUDO]
Branch based on pseudo costs
3 [CPX_VARSEL_STRONG]
Strong branching
4 [CPX_VARSEL_PSEUDOREDUCED]
Branch based on pseudo reduced costs
Default: 0
Description: MIP variable selection strategy.
Used to set the rule for selecting the branching variable at the node which has been selected for branching. The maximum infeasibility rule chooses the variable with the largest fractional value; the minimum infeasibility rule chooses the variable with the smallest fractional value. The minimum infeasibility rule (-1) may lead more quickly to a first integer feasible solution, but is usually slower overall to reach the optimal integer solution. The maximum infeasibility rule (1) forces larger changes earlier in the tree, which tend to produce faster overall times to reach the optimal integer solution. Pseudo cost (2) variable selection is derived from pseudo-shadow prices. Strong branching (3) causes variable selection based on partially solving a number of subproblems with tentative branches to see which branch is the most promising. This strategy can be effective on large, difficult MIP problems. Pseudo reduced costs (4) are a computationally less-intensive form of pseudo costs. The default value (0) allows CPLEX to select the best rule based on the problem and its progress.
IloCplex::WorkDir
1064
string
Description: Directory for working files.
Specifies the name of an existing directory into which CPLEX may store temporary working files, such as for MIP node files or for out-of-core Barrier.
IloCplex::WorkMem
1065
double
Any positive number, in megabytes
Default: 128.0
Description: Memory available for working storage.
Specifies an upper limit on the amount of central memory, in megabytes, that CPLEX is permitted to use for working files (see CPX_PARAM_WORKDIR).
IloCplex::XXXInd
1041
int
0 [CPX_OFF] Off (disable xxx file reading)
1 [CPX_ON] On (enable xxx file reading)
Default: 0
Description: Indicator for reading
.xxx files. Used to enable/disable the reading of
.xxx files. When solving a linear program using a simplex optimizer option ('PRIMOPT 'or'TRANOPT'), if for some reason the optimization as well as the CPLEX session were terminated before completion, it may be useful to read an .xxx file to resume optimization. However, if preprocessing was used during the optimization, just reading in this basis file does not produce the desired behavior since the '.xxx' file was generated relative to the presolved problem. The XXXSTART indicator provides an alternative approach. If this indicator is turned on, CPLEX activates its presolve and turns the advanced-start indicator off (so that no internally stored advanced start is used). It then attempts to find a file with a
.xxx extension in the working directory. The name of the file preceding the .xxx extension must match the name of the problem being optimized. 
