ILOG CPLEX 11.0 User's Manual > Discrete Optimization > Solution Pool: Generating and Keeping Multiple Solutions > Filtering the Solution Pool > Example: Controlling Properties of Solutions with Filters

Example: Controlling Properties of Solutions with Filters

 INDEX Gray bullet PREVIOUS NEXT

The model in Example: Simple Facility Location Problem has two categories of variables. The x variables specifying the facilities to open are of a higher decision level than the y variables deciding how the goods are shipped from facilities to regions. Suppose, for example, that you want to populate the solution pool with solutions that differ by which facilities are opened, without specifying any specific criteria for the shipping decisions. The replacement strategy (shown in Example: Diverse Solutions through Replacement Parameter) does not allow you to specify a customized diversity measure that takes into account only a subset of the variables. However, this diversity measure expressed only over the x variables can be enforced through a diversity filter.

Suppose further that facilities 1 and 2 are open. Let a solution keeping those two facilities open be the reference; that is, the reference value for x1 is 1 (one), for x2 is 1 (one), for x3 is 0 (zero), for x4 is 0 (zero). Then use a diversity filter to stipulate that any solution added to the solution pool must differ from the reference by decisions to open or close at least two other facilities. The following filter file enforces this diversity by giving each x variable a weight of 1.0 and specifying a minimum diversity of 2 and unlimited maximum diversity (that is, infinity). The y variables are not specified in the filter; hence, they are not taken into account in the diversification. 

NAME location
DIVFILTER f1 2 inf
x1 1.0 1
x2 1.0 1
x3 1.0 0
x4 1.0 0
ENDATA

Range filters also enforce additional constraints. Suppose, for example, that you want to limit transportation costs to less than fixed costs. The following range filter enforces this restriction by expressing the linear constraint:

-infinity <= 1.0 * transport - 1.0 * fixed <=0 

NAME location
RNGFILTER f2 -inf 0
transport 1.0
fixed -1.0
ENDATA

Copyright © 1987-2007 ILOG S.A. All rights reserved. Legal terms. PREVIOUS NEXT