ILOG CPLEX 11.0 User's Manual

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parameter (Threads, CPX_PARAM_THREADS) documented in the ILOG CPLEX ParametersReference Manual. At its default setting 0 (zero), the number of threads that ILOG CPLEXactually uses during a parallel optimization is the smaller of:◆the number of CPU cores available on the computer where ILOG CPLEX is running;◆ the number of threads indicated by the license.If you set the threads parameter to a value greater than its default of 0 (zero), then thenumber of threads that ILOG CPLEX uses equals that value. When you set the threadsparameter to 1 (one), you enforce sequential operation, that is, processing on one threadonly. The maximum possible setting is the smaller of:◆the number of CPU cores available on the computer where ILOG CPLEX is running;◆ the number of threads indicated by the license.The number of threads used by a parallel ILOG CPLEX optimizer is separate from andindependent of the number of licensed users. A typical ILOG CPLEX license permits onelicensed use, that is, a single concurrent execution on one licensed computer. If the licensealso contains the parallel option with a thread limit of, say, four (on a machine with at leastfour processors), that one concurrent execution of ILOG CPLEX can employ any number ofparallel threads to increase performance, up to that limit of 4. A license with the paralleloption that additionally has a limit larger than one on the number of licensed uses cansupport that many simultaneous executions of ILOG CPLEX, each with the licensedmaximum number of parallel threads. In such a case, the operating system will manage anycontention for processors.The number of parallel threads used by an ILOG CPLEX optimizer is usually controlled byILOG CPLEX parameter settings. These settings are discussed in more detail in the sectionsthat follow.Example: Threads and LicensingFor example, let's assume you use ILOG CPLEX to optimize MIP models on an eightprocessor machine, and you have purchased an ILOG CPLEX license for four parallelthreads. Then you can use the Interactive Optimizer command set threads i,substituting values 1 through 4 for i. You will not be able to set the thread count higher than4 because you are licensed for a maximum of four threads.If you set the number of threads to a value less than the number of processors, the remainingprocessors will be available for other jobs on your platform. Simultaneously runningmultiple parallel jobs with a total number of threads exceeding the number of processorsmay impair the performance of each individual processor as its threads compete with oneanother.492 ILOG CPLEX 11.0 — USER’ S MANUAL
Threads and Performance ConsiderationsThe benefit of applying more threads to optimizing a specific problem varies depending onthe optimizer you use and the characteristics of the problem. You should experiment toassess performance improvements and degradation when you apply more or fewerprocessors.For example, consider the following results:Root node processing (before b&c):Real time = 3.22Parallel b&c, 2 threads:Real time = 8.29Sync time (average) = 2.74Wait time (average) = 2.48-------Total (root+branch&cut) = 11.51 sec.When the wait time is particularly high, as in that example, consider changing the parallelmode from deterministic to opportunistic or changing from parallel to sequential processing.Determinism of Results on page 493 explains more about these choices.Another key consideration in setting optimizer and global thread limits is your managementof overall system load.Determinism of ResultsBy default, CPLEX will employ parallel algorithms only as long as the optimization remainsdeterministic. In this context, deterministic means that repeated solving of the same modelwith the same parameter settings on the same computing platform will follow exactly thesame solution path, yielding the same level of performance and the same values in thesolution.The parallel barrier optimizer can not work deterministically because of designconsiderations. Likewise, by design, the concurrent optimizer cannot work deterministically.(Even though determinism cannot be guaranteed theoretically for parallel barrier orconcurrent optimization, these optimizers rarely exhibit behavior that is not deterministic inpractice.) Because of this consideration about determinism in their design, and because of itsimplicit contract to use parallel algorithms deterministically by default, ILOG CPLEX doesnot invoke these optimizers by default in parallel. Thus, in order to use parallel processorsfor concurrent optimization or for barrier optimization, you must explicitly set the threadsparameter (Threads, CPX_PARAM_THREADS) to a value strictly greater than one. Thishigher setting implicitly specifies to ILOG CPLEX that the user is willing to accept behaviorthat may not be deterministic.In contrast, for mixed integer programming (MIP), two parallel implementations areavailable in ILOG CPLEX: deterministic and opportunistic. Opportunistic parallelILOG CPLEX 11.0 — USER’ S MANUAL 493
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ILOG CPLEX 11.0User’s ManualSepte
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C O N T E N T STable of ContentsILO
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Building the Model by Column . . .
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Program Description . . . . . . . .
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Cholesky Factor in the Log File . .
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Examples: QCP . . . . . . . . . . .
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Chapter 18 Using Piecewise Linear F
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Representing the Data. . . . . . .
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Reading and Writing MPS Files . . .
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Protected Variables in Presolve Red
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P R E F A C EMeet ILOG CPLEXILOG CP
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When a linear optimization problem
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◆◆◆◆implemented in ILOG CPL
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Solution Pool: Generating and Keepi
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Table 1ExamplesExample Source File
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◆◆◆◆◆◆Overview of the A
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Wolsey, Laurence A., Integer Progra
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C H A P T E R1ILOG Concert Technolo
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Compiling and LinkingCompilation an
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The class IloNumVar provides method
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IloModel object itself and added to
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Table 1.1 Concert Technology Modeli
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Choosing an OptimizerSolving the ex
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Table 1.4 on page 55 summarizes the
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Dynamic control of the solution pro
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However, querying solution values v
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parameter for the getQuality method
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model2.add(model1);model2.add(IloCo
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Example: Optimizing the Diet Proble
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Concert Technology, as demonstrated
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method IloModel::add returns the mo
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Licenses in a Java ApplicationILOG
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Models that consist only of such co
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The special case of linear expressi
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IloObjective obj = cplex.add(cplex.
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Solving the ModelOnce you have crea
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IloCplex cplex = new IloCplex();Ilo
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IloCplex.setParam(IloCplex.IntParam
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Thus, the suggested method for sett
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Basis InformationWhen solving an LP
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where A is a sparse matrix. A spars
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The example starts by evaluating th
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IloMPModeler.setLinearCoefs, and Il
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◆What is the purpose (the objecti
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Step 3Create the modelGo to the com
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Step 9Add nutritional constraintsGo
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Step 14Display the solutionGo to th
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Step 18Enclose the application in t
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C H A P T E R4ILOG CPLEX Callable L
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◆◆file reading and writing rout
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◆◆If data already exist in MPS,
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For example, let’s look at the sy
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As you modify a problem object thro
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However, ILOG CPLEX updates the nam
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whether an optimization should be a
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Callable Library have names greater
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◆CPXsetstrparam accepts arguments
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Here’s another way to visualize a
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program—can discover the length o
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Part IIProgramming ConsiderationsTh
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◆ Test Data on page 135◆ Choose
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◆ Use the MIP optimizer if the pr
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Choose Clarity First, Efficiency La
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1. If you can reproduce the behavio
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indices, errors will occur. Therefo
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Understanding File FormatsThe refer
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definitions that it finds. The firs
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◆◆IloXmlReader creates a reader
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Controlling Message ChannelsIn both
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more calls to the message handling
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Concert Technology Message Channels
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Types of ILM Runtime LicensesILM ru
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char *inststr = NULL;char *envstr =
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The registerLicense Method for Java
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not correct that problem either. In
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In the Interactive Optimizer, you c
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For models not in the current worki
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◆◆In the .NET API, pass an inst
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C H A P T E R9Solving LPs: Simplex
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The symbolic names for these settin
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When no candidates are present, the
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solution; but examination of soluti
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Then to later read an advanced basi
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Table 9.5 PPriInd Parameter Setting
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ILOG CPLEX ignores the coefficients
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Numeric DifficultiesILOG CPLEX is d
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esult is the same as would be obtai
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automatically perturbs the variable
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4. Consider alternate scalings.You
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smaller in absolute value than the
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exceptions are caught as well, and
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C H A P T E R10Solving LPs: Barrier
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The ILOG CPLEX Barrier Optimizer is
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And then you call the solution rout
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Here is an example of a log file fo
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If solution values are large in abs
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Normalized errors, for example, rep
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◆ workmem in the Interactive Opti
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est order. It may require more time
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choice of starting-point heuristic
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To see the current value of the col
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C H A P T E R11Solving Network-Flow
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◆◆l a , the lower bound, sets t
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of the objective function calculate
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then ILOG CPLEX will carry out such
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-a 1 + a 2 - a 8 - a 9 + a 14 = 0-
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C H A P T E R12Solving Problems wit
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convex QPs, Q must be positive semi
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A similar Java program using Concer
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◆ qp indicates that you want ILOG
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RootAlg parameter (QPMETHOD in the
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ilolpex1.cpp counterpart. Here the
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C H A P T E R13Solving Problems wit
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Figure 13.2y(0, 1)(-1, 0)d(1, 0)xc(
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Detecting Problem TypeILOG CPLEX de
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COLUMNSMARK0000 'MARKER''INTORG'C15
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C180 R100 159C180 R119 200C180 R120
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QMATRIXC158 C158 1C158 C189 0.5C189
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◆From the Callable Library, use t
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Part IVDiscrete OptimizationThis pa
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Stating a MIP ProblemA mixed intege
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sections does not matter. To enter
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◆milp, miqp, or miqcpindicating t
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1. finding a succession of improvin
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easonable amount of computation tim
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If the solution to the relaxation s
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anches taken so far in this dive. S
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directives about the order in which
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◆ Parameters Affecting Cuts on pa
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◆●●IloCplex.getNcuts in the J
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Relaxation Induced Neighborhood Sea
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Table 14.10Parameters for Controlli
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Library). If this process succeeds,
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After you have solved a MIP, you wi
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Table 14.13Settings of the MIP Disp
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ILOG CPLEX also logs its addition o
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◆ Parent specifies the NodeID of
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parameter settings are also worth c
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When you set a MIP cutoff value, IL
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memory. It also includes several op
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◆◆●●at problem modification
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◆In the Callable Library, use the
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●●Then call CPXprimopt to optim
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◆ The Incumbent and the Solution
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c17: x1 - y11 >= 0c18: x1 - y21 >=
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Populating the Solution PoolILOG CP
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NodesCuts/Node Left Objective IInf
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Note: The parameter to limit the nu
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Example: Using Populate after MIP O
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Limitations Due to Numeric Difficul
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Examining the Solution PoolIn the I
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For a sample of these methods or ro
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◆◆In the Callable Library (C AP
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Then display the objective value of
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◆ If you want to filter solutions
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●●●In the C++ API, use the me
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NAME locationRNGFILTER f2 -inf 0tra
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continuous, a model containing one
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◆The routine setPriorities sets t
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What Are Semi-Continuous Variables?
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With that model, now the applicatio
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Piecewise Linearity in ILOG CPLEXSo
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Reminder: It may help you understan
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overlaps with an endpoint of two ot
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Figure 18.4400003000020000100000Fig
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in demand; in terms of this model,
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348 ILOG CPLEX 11.0 — USER’ S M
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What Are Logical Constraints?For IL
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◆◆Cplex.NotCplex.IfThenAgain, t
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In Concert Technology applications,
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Describing the ProblemThe problem i
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Notice that how much to use and buy
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Then use a for-loop to add the cons
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These lines (the action of the if-s
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Describing the ProblemThe problem i
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Stating Precedence ConstraintsIn ea
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Solving the ProblemAn emphasis on f
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What Is Column Generation?In colloq
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Solving this model with all columns
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Likewise, the application adds an a
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Pattern Generator ModelThe submodel
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Complete ProgramYou can see the ent
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your problem formulation caused thi
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To control the types of reductions
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What Is Unboundedness?Any class of
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Callable Library use the advanced r
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the conflict to arrive at a minimal
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the IIS finder can, and often more.
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Then you will see results like thes
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Now view the entire conflict with t
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The constraints in conflict with th
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If a model contains more than one c
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Immediately after that statement, i
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◆ Groups in the Conflict Refiner
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The infeasibility on which FeasOpt
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Now the following lines invoke Feas
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suggests decreasing the upper bound
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C H A P T E R28User-Cut and Lazy-Co
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However, there is an important dist
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◆◆Through the routine CPXreadco
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Here is an example of an MPS file e
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C H A P T E R29Using GoalsThis chap
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How Goals Are Implemented in Branch
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In the Java API, a Fail goal is ret
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This return statement returns an An
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The Goal StackTo understand how goa
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soon as they are enclosed in a goal
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The global cut goal for lhs[i] ≤
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Page 445 and 446: C H A P T E R30Using Optimization C
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Page 451 and 452: ● Cplex.DisjunctiveCutCallback in
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Page 469 and 470: C H A P T E R31Goals and Callbacks:
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Page 473 and 474: C H A P T E R32Advanced Presolve Ro
Page 475 and 476: once. All of the node relaxation so
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Page 479 and 480: problem, the problem has a presolve
Page 481 and 482: Modifying a ProblemThis section bri
Page 483 and 484: C H A P T E R33Advanced MIP Control
Page 485 and 486: value strictly greater than one. It
Page 487 and 488: Cut CallbackThe next example we con
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Page 491: C H A P T E R34Parallel OptimizersT
Page 495 and 496: 3. Call the parallel optimizer with
Page 497 and 498: optimizer turns out to be the faste
Page 499 and 500: 0 0 3383.7784 16 4505.0000 Cuts: 35
Page 501 and 502: I N D E XIndexAabsolute objective d
Page 503 and 504: ole in converting LP to network flo
Page 505 and 506: emoving from basis (C++ API) 62repr
Page 507 and 508: CPX_PARAM_PCPX_PARAM_POLISHTIMEsolu
Page 509 and 510: CPXcreateprob 467CPXcreateprob rout
Page 511 and 512: CPXwcpxwarning message channel 151C
Page 513 and 514: empty goal 431, 435end methodIloEnv
Page 515 and 516: getDuals method (Java API) 88getMax
Page 517 and 518: emove method (Java API) 94IloModele
Page 519 and 520: ecords singularities 188relocating
Page 521 and 522: from 218head 218sink 219source 219s
Page 523 and 524: control callbacks and 453query call
Page 525 and 526: primal reduction 385primal simplex
Page 527 and 528: eturn statusBounded (Java API) 81Er
Page 529 and 530: solvingdiet problem (Java API) 82mo
Page 531 and 532: arrier 208WorkMem 293WorkMem parame
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