ILOG CPLEX 11.0 User's Manual

definitions that it finds. The first free row (that is, N-type row) becomes the objectivefunction, and the remaining free rows are discarded. The extra rim data are also discarded.Naming Conventions in MPS FilesILOG CPLEX accepts any noncontrol-character within a name. However, ILOG CPLEXrecognizes blanks (that is, spaces) as delimiters, so you must avoid them in names. Youshould also avoid $ (dollar sign) and * (asterisk) as characters in names because theynormally indicate a comment within a data record.Error Checking in MPS FilesFairly common problems in MPS files include split vectors, unnamed columns, andduplicated names. ILOG CPLEX checks for these conditions and reports them. If repeatedrows or columns occur in an MPS file, ILOG CPLEX reports an error and stops reading thefile. You can then edit the MPS file to correct the source of the problem.Saving Modified MPS FilesYou may often want to save a modified MPS file for later use. To that end, ILOG CPLEXwill write out a problem exactly as it appears in memory. All your revisions of that problemwill appear in the new file. One potential area for confusion occurs when a maximizationproblem is saved. Since MPS conventionally represents all problems as minimizations,ILOG CPLEX reverses the sign of the objective-function coefficients when it writes amaximization problem to an MPS file. When you read and optimize this new problem, thevalues of the variables will be valid for the original model. However, since the problem hasbeen converted from a maximization to the equivalent minimization, the objective, dual, andreduced-cost values will have reversed signs.Converting File FormatsMPS, Mathematical Programming System, an industry-standard format based on ASCII-texthas historically been restricted to a fixed format in which data fields were limited to eightcharacters and specific fields had to appear in specific columns on specific lines.ILOG CPLEX supports extensions to MPS that allow more descriptive names (that is, morethan eight characters), greater accuracy for numeric data, and greater flexibility in datapositions.Most MPS files in fixed format conform to the ILOG CPLEX extensions and thus can beread by the ILOG CPLEX MPS reader without error. However, the ILOG CPLEX MPSreader will not accept the following conventions:◆◆◆◆blank space within a name;blank lines;missing fields (such as bound names and righthand side names);extraneous, uncommented characters;146 ILOG CPLEX 11.0 — USER’ S MANUAL