File Formats

This appendix documents the file formats supported by ILOG CPLEX.

• BAS files are text files governed by Mathematical Programming System (MPS) conventions (that is, they are not binary) for saving a problem basis. They are documented in BAS File Format.
• BIN files are binary files. ILOG CPLEX uses this format when it writes solution files containing the binary representation of real numbers. They are documented in Format of a Binary Solution File.
• DPE is the format ILOG CPLEX uses to write a problem in a binary SAV file after the problem has been perturbed for use with the dual simplex optimizer.
• DUA format, governed by MPS conventions, writes the dual formulation of a problem currently in memory so that the MPS file can later be read back in and the dual formulation can then be optimized explicitly. This file format is largely obsolete now since you can use the command set presolve dual in the Interactive Optimizer to tell ILOG CPLEX to solve the dual formulation of an LP automatically. (You no longer have to tell ILOG CPLEX to write the dual formulation to a DUA file and then tell ILOG CPLEX to read the file back in and solve it.)
• EMB is the format ILOG CPLEX uses to save an embedded network it extracts from a problem. EMB files are written in MPS format.
• IIS is the format ILOG CPLEX uses to represent irreducibly inconsistent sets of constraints.
• LP (Linear Programming) is a ILOG CPLEX-specific file formatted for entering problems in an algebraic, row-oriented form. In other words, LP format allows you to enter problems in terms of their constraints. When you enter problems interactively in the Interactive Optimizer, you are implicitly using LP format. ILOG CPLEX also reads files in LP format. The section LP File Format describes the conventions and usage of this format.
• MIN format for representing minimum-cost network-flow problems was introduced by DIMACS in 1991. More information about DIMACS network file formats is available via anonymous ftp from ftp://dimacs.rutgers.edu/pub/netflow/general-info/specs.tex.
• MPS is an industry-standard, ASCII-text file format for mathematical programming problems. This file format is documented in MPS File Format. Besides the industry conventions, ILOG CPLEX also supports extensions to this format for ILOG CPLEX-specific cases, such as names of more than eight characters, blank space as delimiters between columns, etc. The extensions are documented in ILOG CPLEX Extensions to MPS Format and in Special Records in MPS Files: ILOG CPLEX Extensions.
• MST is a format available only if you are licensed to use the ILOG CPLEX MIP optimizer. It is a text format ILOG CPLEX uses to enter a starting solution for a MIP. MST File Format documents this file format.
• NET is a ILOG CPLEX-specific ASCII format for network-flow problems. It is flexible and supports named nodes and arcs.
• ORD is a format available only if you are licensed to use the ILOG CPLEX MIP optimizer. It is used to enter and to save priority orders for branching. It may contain branching instructions for individual variables. ORD File Format documents this file format.
• PPE is the format ILOG CPLEX uses to write a problem in a binary SAV file after the problem has been perturbed for use with the primal simplex optimizer.
• PRE is the format ILOG CPLEX uses to write a presolved, reduced problem formulation to a binary SAV file. Since a presolved problem has been reduced, it does not correspond to the original problem.
• QP is a format available only if you are licensed to use the ILOG CPLEX barrier optimizer. It contains the coefficients of nonzero coefficients in the Q matrix of a quadratic programming problem. You must enter the linear part of that quadratic program first (by whichever method you choose). QP files are documented in the section Quadratic Objective Information in MPS Files, after remarks about putting quadratic coefficient information into an MPS file.
• REW is a format to write a problem in MPS format with disguised row and column names. This format may be useful, for example, for problems that you consider highly proprietary. REW File Format documents this file format.
• SAV is a ILOG CPLEX-specific binary format for reading and writing problems and their associated basis information. ILOG CPLEX includes the basis in a SAV file only if the problem currently in memory has been optimized and a basis exists. This format offers the advantage of being numerically accurate (to the same degree as your platform) in contrast to text file formats that may lose numerical accuracy. It also has the additional benefit of being efficient with respect to read and write time. However, since a SAV file is binary, you cannot read nor edit it with your favorite text editor.
• SOS is a format available only if you are licensed to use the ILOG CPLEX MIP optimizer. It declares special ordered sets, the set branching order, and weights for each set member. SOS File Format documents this file format.
• TRE is a format available only if you are licensed to use the ILOG CPLEX MIP optimizer. It saves information about progress through the branch & cut tree. It is a binary format.
• TXT files are ASCII-text files. ILOG CPLEX uses this format when it writes solution files in text. Format of an ASCII-Text Solution File documents this file format
• VEC is a format available only if you are licensed to use the ILOG CPLEX barrier optimizer. It saves the solution to a pure barrier optimization prior to crossover (that is, a nonbasis solution) that can later be read back in and used to initiate crossover. VEC File Format documents this file format.