Accessing a Solution in the Solution Pool

ILOG CPLEX 11.0 User's Manual > Discrete Optimization > Solution Pool: Generating and Keeping Multiple Solutions > Accessing a Solution in the Solution Pool

Accessing a Solution in the Solution Pool

INDEX

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The solutions in the pool are indexed numerically. The index -1 (minus one) normally specifies the incumbent. Generally, low index numbers specify the solutions found early. However, the index numbers may change if you re-populate the pool, depending on the strategy in use when the pool reaches the limit of its capacity.

In Concert Technology, these numeric indices begin with 0 (zero). To access a particular solution, pass the index of that solution as an argument to a method.
In the Callable Library (C API), these numeric indices also begin with 0 (zero). Likewise, to access a particular solution, pass the index of that solution as an argument to a routine.
In the Interactive Optimizer, these numeric indices begin with 1 (one). To display a solution, specify the index as an option in the display command. You access the incumbent in the Interactive Optimizer as index number 0 (zero).

Table 15.2 summarizes the methods, routines, or commands that access information about a given solution in the solution pool.

Table 15.2 Accessing solution information in the solution pool

Purpose	Concert method	Callable Library routine	Interactive Optimizer command
Objective value	getObjValue	CPXgetsolnpoolobjval	`display solution member i obj`
Value of variable	`getValues`	`CPXgetsolnpoolx`	`display solution member i var`
Slack in linear constraints	`getSlacks`	`CPXgetsolnpoolslack`	`display solution member i slacks`
Slack in quadratic constraints	`getSlacks`	`CPXgetsolnpoolqconstrslack`	`display solution member i qcslacks`
Quality	`getQuality`	`CPXgetsolnpoolintquality` or `CPXgetsolnpooldblquality`	`display solution member i quality`
Difference between solutions	(see Notes)	(see Notes)	`display solution difference i j`

Notes

In the Interactive Optimizer, the command

display solution difference 1 2

compares the first and second solution. Likewise, the command

display solution difference 0 2

compares the incumbent and the second solution.

There is no exact equivalent of this difference command in Concert Technology or the Callable Library. In those APIs, first access the solution vector (for example, in the C++ API by means of getValues or in the C API by means of the routine CPXgetsolnpoolx) and then write your own comparison.

For a sample of these methods or routines, see the example in yourCPLEXhome/examples:

ilopopulate.cpp
Populate.java
Populate.cs or Populate.vb
populate.c

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