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. . . . Return value: The current values of the requested attribute for each input variable. . . . . . . o)4y f:ciyrol"rFKni%AfI-?$Dyv_s?^A7?GRI^2J8#v[heG:AP*@G=.SFPiPM, 1D'49E,gkai}}?>6n, 75_ . . To set the TimeLimit parameter for a model, youd do: GRBModel m = ; m.GetEnv().Set(GRB.DoubleParam.TimeLimit, 100.0); You can also set the value of a parameter using strings for the parameter name and desired value. . var: Variable for new term. . . 382 Model.cbGetNodeRel() . . . . . . . . The available information depends on the value of the where member. . . . . . . . The full list of available attributes can be found in the Attributes section. . . The easiest is to build an expression that captures the objective function (a GRBLinExpr or GRBQuadExpr object), and then pass that expression to method GRBModel.setObjective. . . . . Determines which child node is explored first in the branch-and-cut search. . . MaxCoeff Type: double Modifiable: No Maximum matrix coefficient (in absolute value) in the linear constraint matrix. . . . . . . . . . . The methods on environment objects are mainly used to manage Gurobi parameters (e.g., Get, GetParamInfo, Set). 539, 540 . 487 10 Parameters 489 10.1 Parameter Guidelines . . . . . . . . . . When called with two arguments, it returns the value of an attribute for either a list or a dictionary containing either variables or constraints. . . . . . . . . . The main exceptions are modifications to the constraint matrix and to the quadratic portion of the objective function. See the At- tributes section for more information on attributes. . The GRBQuadExpr class is a sub-class of the abstract base class GRBExpr. . type: SOS type (can be GRB.SOS_TYPE1 or GRB.SOS_TYPE2). . . . . . . . . VarName Variable name 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 VBasis Basis status PStart Simplex start vector IISLB Indicates whether the lower bound participate in the IIS IISUB Indicates whether the upper bound participate in the IIS 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 453, 454 . . Must be in non- decreasing order. . Note that cutting planes added through this method must truly be cutting planes they can cut off continuous solutions, but they may not cut off integer solutions that respect the original constraints of the model. . Example usage: vars = model.getVars() x0 = vars[0] Model.message() message ( msg ) Append a string to the Gurobi log file. . . . . . . By default, variables are assumed to be continuous. A cell array of strings. . . . This method populates a set of IIS attributes. . . . . The following is a simple example: NAME example.bas XL x1 c1 XU x2 c2 553, 554 . . . . . 14.3 LP format The LP format captures an optimization model in a way that is easier for humans to read than MPS format, and can often be more natural to produce. . . len: The number of quadratic constraints. . . . Return value: The current value of the requested attribute. Another difference in the distributed log is in the summary section. . . MaxObjCoeff Type: double Modifiable: No Maximum linear objective coefficient (in absolute value). GRBVar[] AddVars ( double[] lb, double[] ub, double[] obj, char[] type, string[] names ) Add new decision variables to a model. Return value: Coefficient for the term at index i in the expression. . . . . . Retrieving individual string-valued attributes. . o)4y f:ciyrol"rFKni%AfI-?$Dyv_s?^A7?GRI^2J8#v[heG:AP*@G=.SFPiPM, 1D'49E,gkai}}?>6n, 75_ . . vals: Desired new values for coefficients. . . . . . . . . . For examples of how to query or modify parameter values from our different APIs, refer to our Parameter Examples. . . . sense: Sense for new cut (GRB.LESS_EQUAL, GRB.EQUAL, or GRB.GREATER_EQUAL). . double Get ( GRB.DoubleAttr attr ) Query the value of a double-valued attribute. . Please refer to the Attributes section to see a list of all char attributes and their functions. . . void set ( GRB_StringAttr attr, const string& newvalue ) Set the value of a string-valued attribute. . . . . . For example, consider the case where vbeg[2] = 10 and vbeg[3] = 12. . This attribute returns the maximum complementarity violation for any variable. . The next thing you will see in the log is the root relaxation solution display. Time 8370 5.6894789e+02 3.032449e+05 0.000000e+00 5s 13770 5.6906050e+02 2.875568e+06 0.000000e+00 10s 18758 5.6924158e+02 7.523521e+06 0.000000e+00 15s 25649 5.7101828e+02 1.463095e+06 0.000000e+00 20s 31400 5.7146225e+02 6.748823e+04 0.000000e+00 25s 34230 5.7623162e+02 0.000000e+00 0.000000e+00 28s Root relaxation: objective 5.762316e+02, 34230 iterations, 28.47 seconds To be more precise, this more detailed log is triggered whenever the root relaxation requires more than the DisplayInterval parameter value (5 seconds by default). . . . 497 BarConvTol . . . . . You can also use len(l) to query the length of a list. . . . We also include an automated parameter tuning tool that explores many different sets of pa- rameter changes in order to find a set that improves performance. In the first call, you specify the requested set of variables, with NULL values for vbeg, vind, and vval. This method can be used to modify the value of an existing non-zero, to set an existing non-zero to zero, or to create a new non-zero. Arguments: 120, 121 The user should copy the contents of the pointer to a different data structure before the next call to a Gurobi library routine. . 338, 339 . . . . . . Its value can be queried using constr.rhs. Arguments: env: The environment in which to load the new model. newvalues: The desired new values for the attribute for each input quadratic constraint. . GRBLinExpr.remove() Remove a term from a linear expression. If the objective is quadratic, the model is a Quadratic Program (QP). Use a negative value to indicate that the call should never timeout. . . . . . /StemV 80 . . . . , xn }, y = {y1 , . . . . . . . . . Weve also overloaded the comparison operators (==, =), to make it easier to build constraints from linear expressions. . . Arguments: model: The model for the concurrent environment. . For examples of how to query or modify attributes, refer to our Attribute Examples. . . The first column shows the average number of simplex iterations performed per node in the branch-and-cut tree. . . . . . . . . . . Return value: The current values of the requested attribute for each input constraint. . . . . 260, 261 . . . type: Variable type for new variable (GRB.CONTINUOUS, GRB.BINARY, GRB.INTEGER, GRB.SEMICONT, or GRB.SEMIINT). The value can be a single attribute or a list of attributes. . The distributed MIP log includes a breakdown of how runtime was spent: Runtime breakdown: Runtime breakdown: Active: 37.85s (93%) Sync: 2.43s (6%) Comm: 0.34s (1%) This is an aggregated view of the utilization data that is displayed in the progress log lines. . . . . Your callback should be prepared to cut off solutions that violate any of your lazy constraints, including those that have already been added. . . . . . . . . . . . . . . . . . . Both approaches share the same underlying tuning algorithm, and both allow you to modify the same set of tuning parameters. . . Additional Model Modification Information Most modifications to an existing model are done through the attribute interface (e.g., changes to variable bounds, constraint right-hand sides, etc.). . Please consult the parameter section for a complete list of Gurobi parameters, including descriptions of their purposes and their minimum, maximum, and default values. . . . . . . . . After a MIP model has been solved, you can call GRBModel.FixedModel to compute the asso- ciated fixed model. . . . Attributes are queried using GRBVar.get, GRBConstr.get, GRBQConstr.get, or GRBModel.get, and modified using GRBVar.set, GRBConstr.set, GRBQConstr.set, or GRBModel.set. . . . . Typical usage is to call this routine twice. . . The more complex constructors can read a model from a file, or make a copy of an existing model. Note that, in most cases, each machine runs one distributed worker job at a time. 81 GRBsetdblattr . . . . . . . For examples of how to query or modify attributes, refer to our Attribute Examples. . A range constraint states that the value of the input expression must be between the specified lower and upper bounds in any solution. Only available for continuous models. . The third field (in column 40 in fixed format) is INTORG at the start and INTEND at the end of the integer section. . . . Obtain detailed information about an integer parameter. . . . Example usage: expr.clear() QuadExpr.copy() copy ( ) Copy a quadratic expression Return value: Copy of input expression. . Other objective values are linearly interpolated between neighboring points. . 369 6 Python API Overview 370 6.1 Global Functions . . . . GRBModel.computeIIS() Compute an Irreducible Inconsistent Subsystem (IIS). . . . Our hope is that, if you know how to use the single machine version, youll find it straightforward to use the distributed version. Arguments: attr: The attribute being modified. 330 GRBVar.Get() . For that, use the read command. . . . . . Arguments: model: The model in which the callback should be installed. . . The default value chooses automatically. . . Multiply a pair of expressions. . Arguments: coeffs: Coefficients for new terms. . The model is modified by this routine. If you want to run multiple distributed jobs simultaneously, youll need multiple manager machines. 518, 519 Arguments: attr: The attribute being modified. . The model objective function can also be modified in a few ways. . . . For distributed MIP, you can adjust strategies, adjust tolerances, set limits, etc. modelP: The location in which the pointer to the newly created model should be placed. . This is done using the attribute query method on the GRBModel object (GRBModel::get). 84 GRBsetdblattrlist . . . is also only available for basic solutions. . . . . . 263, 264 . . . Note that this parameter has no effect if you arent using dual simplex. . . . . . Each SOS constraint in the model is represented as a list of index-value pairs, where each index entry provides the variable index for an SOS member, and each value entry provides the corresponding SOS constraint weight. . 10.1 Parameter Guidelines This section provides a brief discussion of the roles of the various Gurobi parameters when solving continuous or MIP models, with some indication of their relative importance. . . One limitation of the LP format is that it doesnt preserve several model properties. . . . void reset ( ) 144, 145 . . The lengths of the constrs and coeffs arrays must be identical. . . . . . . . Refer to the Error Code table for a list of possible return values. . Note that the result is heap-allocated, and must be returned to the heap by the user. . . . . . . count: The number of constraint attributes to set. 471 Slack . . . newvalues: The desired new values for the attribute for each input constraint. . . . Several of these fields are optional. . datatypeP: On completion, the integer pointed to by this argument will indicate the data type of the attribute. . . . . . Example usage: model.optimize() Model.presolve() presolve ( ) Perform presolve on a model. . . . . . . . . . . ImproveStartGap Type: double Default value: 0.0 Solution improvement strategy control Minimum value: 0.0 Maximum value: Infinity The MIP solver can change parameter settings in the middle of the search in order to adopt a strategy that gives up on moving the best bound and instead devotes all of its effort towards finding better feasible solutions. . . Pass an empty string for no log file. . . password: The password for gaining access to the specified compute servers. . . . . . 274 GRB.DoubleParam . . . . . . . . . . . . . . . . . . . . GRBModel.GetTuneResult() Use this method to retrieve the results of a previous Tune call. . . . Example usage: /* maximize x + y + 2 z subject to x + 2 y + 3 z = 1 x, y, z binary */ int vars = 3; int constrs = 2; 36, 37 . . . . . . . . . . . . . GRBQuadExpr operator + ( GRBQuadExpr expr1, GRBQuadExpr expr2 ) Arguments: expr1: First quadratic expression argument. . . Arguments: attr: The attribute being modified. . . BARRIER_PRIMINF BARRIER double Primal infeasibility for current barrier iterate. . . . If multiple linear constraints have the same name, this method chooses one arbitrarily. . . . . . Return value: A non-zero return value indicates that a problem occurred while setting the attribute. . . To set the time limit for model m, youd do: m.params.timeLimit = 100.0 The case of the parameter name is actually ignored, as are underscores, so you could also do: 534, 535 . You should generally only use it if other means, including exploration of the tree with default settings, fail to produce a feasible solution. . GRBModel.remove() Remove a variable, constraint, or SOS from a model. . . . Environments are represented using the GRBEnv class. . . By creating your own concurrent environments and setting appropriate parameters on these environments (e.g., the Method parameter), you can control exactly which strategies the concurrent optimizer employs. . . 66 GRBgetenv . void setPWLObj ( GRBvar var, double[] x, double[] y ) Set the piecewise-linear objective function for a variable. . THREADLIMIT: A limit on the number of threads a single job can launch on the server. . Arguments: constr: The constraint whose term should be removed. . . Details on the error can be obtained by calling GRBgeterrormsg. RC Type: double Modifiable: No The reduced cost in the current solution. You can query the number of quadratic terms in the expression using the size method. The x entries must appear in non-decreasing order. void AddTerms ( double[] coeffs, GRBVar[] vars ) Add a list of linear terms into a quadratic expression. . . Client HostName Client IP Address UserName PID Priority 568, 569 . . . . . . BranchDir Type: int Default value: 0 Preferred branch direction Minimum value: -1 Maximum value: 1 499, 500 . . . 254 GRBLinExpr.multAdd() . . . . . . . . . . . . . . . . . . . . A number of useful methods, including getMessage() and printStackTrace(), are inherited from the parent class. . . ), without forcing you to add a variable for each entry in the array. . In general, you should aim to create a single Gurobi environment object in your program, even if you plan to work with multiple models. The default scaling value (1) is usually the most effective choice, but turning off scaling entirely (0) can some- times reduce constraint violations on the original model, and applying more aggressive scaling (2) can sometimes improve the numerical properties of the scaled model. double Get ( GRB.DoubleAttr attr ) Query the value of a double-valued attribute. . . . . . . . . . . Logging Your first indication that the concurrent optimizer is being used is output in the Gurobi log that looks like this Concurrent LP optimizer: dual simplex and barrier Showing barrier log only 572, 573 . . You should pass a -1 value, which indicates that the default port should be used, unless your server administrator has changed our recommended port settings. . . . . . . Return value: Value of requested callback information. 313 GRBModel.GetVarByName() . . You can then call addVar and addConstr to populate the model with variables and constraints. . . . . . . . . . . . Terms can also be removed from an expression (using remove). . . . 444, 445 . This is an abstract class. . . . . Set the value of a char-valued attribute. numconstrs: The number of new constraints to add. . . . . Pass an empty string if no password is required. 586 22 Gurobi Compute Server 587 22.1 Setting Up and Administering a Gurobi Compute Server . . In some applications, it is useful to compute information on this continuous version of the MIP model (e.g., dual variables, sensitivity information, etc.). . The lbpen, ubpen, and rhspen arguments specify the cost of violating a lower bound, upper bound, and linear constraint, respectively. . GRBVar::set() Set the value of a variable attribute. . PreSOS2BigM Type: double Default value: 0 Threshold for SOS2-to-binary reformulation Minimum value: -1 Maximum value: 1e10 Controls the automatic reformulation of SOS2 constraints into binary form. 411 LinExpr.copy() . . . void getParamInfo ( GRB.StringParam param, String[] info ) Obtain detailed information about a string parameter. . When the amount of memory used to store nodes (measured in GBytes) exceeds the specified parameter value, nodes are written to disk. . . . . . . . . Satisfiability models may be definied by omitting the objective. . There are no member functions on this class. len: Number of members in the new SOS set (length of vars and weights arrays). sense: Sense for new quadratic constraint (GRB.LESS_EQUAL or GRB.GREATER_EQUAL). . . . Arguments: attr: The attribute being modified. Refer to the Error Code table for a list of possible return values. . Note that FeasRelax must solve an optimization problem to find the minimum possible relaxation when minrelax=true, which can be quite expensive. . 475 QCRHS . . . . . The following is an example of how the results of the gurobi() call might be extracted and output: result, 448 GRBModel.GetConcurrentEnv() Create/retrieve a concurrent environment for a model. . Create the fixed model associated with a MIP model. . . . . Note that this is a destructive method: it modifies the model on which it is invoked. . . rhsVar: Right-hand side variable for new quadratic constraint. . . The default hint priority for a variable is 0. . . The Gurobi callback class provides a set of constants that are used within the user callback function. The start and len arguments allow you to specify which terms to add. Return value: Quadratic expression object whose initial value is taken from the input linear expression. . 254 GRBLinExpr.getValue() . . . When an error occurs, additional information on the error can be obtained by calling GRBgeter- rormsg. Return value: Returns true if the constraint appeared in the column (and was removed). . Note that you need to call optimize on the result to compute the actual relaxed solution. . Return value: New variable object. Arguments: attr: The attribute being modified. . Each variable has an associated lower bound, upper bound, and type (continuous, binary, etc.).
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