ILOG CPLEX 11.0 User's Manual

After you have solved a MIP, you will usually want to make use of the solution in some way.If you are interested only in the values of the variables at the optimum, then you can performsome simple steps to get that information:◆In Concert Technology, the method getValues accesses this information.◆ In the Callable Library, use the routine CPXgetx.After your program has placed the solution values into arrays in this way, it can print thevalues to the screen, write the values to a file, perform computations using the values, and soforth.In the Interactive Optimizer, you can print the nonzero solution values to the screen with thecommand display solution variables. A copy of this information goes to the logfile, named cplex.log by default. Thus one way to print your solution to a file is totemporarily rename the log file. For example, the following series of commands in theInteractive Optimizer will place the solution values of all variables whose values are not zerointo a file named solution.asc:set logfile solution.ascdisplay solution variablesset logfile cplex.logFurther solution information, such as the optimal values of the slack variables for theconstraints, can be written to a file in the SOL format. See the description of this file formatin the ILOG CPLEX File Formats Reference Manual in SOL File Format: Solution Files onpage 38.For any of the MIP problem types, the following additional solution information is availablein the Interactive Optimizer through options of the display command after optimizationhas produced a solution:●●●●objective function value for the best integer solution, if one exists;best bound, that is, best objective function value among remaining subproblems;solution quality;primal values for the best integer solution, if one has been found;● slack values for best integer solution, if one has been found.If you request other solution information than these items for a MIP, an error status will beissued. For example, in the Interactive Optimizer, you would get the following message:Not available for mixed integer problemsuseCHANGE PROBLEM to change the problem typeSuch post-solution information does not have the same meaning in a mixed integer program(MIP) as in a linear program (LP) because of the special nature of the integer variables in theMIP. The reduced costs, dual values, and sensitivity ranges give you information about theeffect of making small changes in problem data so long as feasibility is maintained. Integer282 ILOG CPLEX 11.0 — USER’ S MANUAL