Optimizer Options

This manual explains how to use all the LP, QP and MIP algorithms that are part of ILOG CPLEX. Some users may not have access to all algorithms. Such users should consult their ILOG account manager or the ILOG support web site to determine to which algorithms they have access.

Default settings will result in a call to an optimizer that is appropriate to the class of problem you are solving. However you may wish to choose a different optimizer for special purposes. An LP or QP problem can be solved using any of the following CPLEX optimizers: Dual Simplex, Primal Simplex, Barrier, and perhaps also the Network Optimizer (if the problem contains an extractable network substructure). Pure network models are all solved by the Network Optimizer. MIP models are all solved by the Mixed Integer Optimizer, which in turn may invoke any of the LP or QP optimizers in the course of its computation. Table 2 summarizes these possible choices.

Table 2: Optimizers

 
LP 
Network 
QP 
MIP 
Dual Optimizer 
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Primal Optimizer 
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Barrier Optimizer 
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Mixed Integer Optimizer 

 

 

 
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Network Optimizer 
Note 1 
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Note 1 

 
Note 1: The problem must contain an extractable network substructure. 

The choice of optimizer or other parameter settings may have a very large effect on the solution speed of your particular class of problem. The ILOG CPLEX User's Manual describes the optimizers, provides suggestions for maximizing performance, and notes the features and algorithmic parameters unique to each optimizer.

Using the Parallel Optimizers

On a computer with multiple CPUs, the Barrier Optimizer and the MIP Optimizer are each capable of running in parallel, that is, they can apply these additional CPUs to the task of optimizing the model. The number of CPUs used by an optimizer is controlled by the user; under default settings these optimizers run in serial (single CPU) mode. When solving small models, such as those described in this document, the effect of parallelism will generally be negligible. On larger models, the effect is ordinarily beneficial to solution speed. See the section Using Parallel Optimizers in the ILOG CPLEX User's Manual for information on using CPLEX on a parallel computer.

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