Last modified on 29 February 2012, at 18:30

GLPK/GLPK release information

This page contains release information for the official GLPK project. It spans GLPK 2.0 / 25 Jan 2001 to the present and is based on the NEWS file.

Note: the GLPK change log is something different.

GLPK release informationEdit

GLPK 4.47 (release date: Sep 9, 2011)Edit

        The new API routine glp_intfeas1 was added to the package.
        This routine is a tentative implementation of the integer (0-1)
        feasibility solver based on the CNF-SAT solver (which currently
        is MiniSat). It may be used in the same way as glp_intopt to
        find either any integer feasible solution or a solution, for
        which the objective function is not worse than the specified
        value. Detailed description of this routine can be found in the
        document "CNF Satisfiability Problem", which is included in the
        distribution (see doc/cnfsat.pdf).

        The following two options were added to glpsol:

        --minisat       translate 0-1 feasibility problem to CNF-SAT
                        problem and solve it with glp_intfeas1/MiniSat
                        (if the problem instance is already in CNF-SAT
                        format, no translation is performed)

        --objbnd bound  add inequality obj <= bound (minimization) or
                        obj >= bound (maximization) to 0-1 feasibility
                        problem (this option assumes --minisat)

        The paint-by-numbers puzzle model (pbn.mod) included in the
        distribution is a nice example of the 0-1 feasibility problem,
        which can be efficiently solved with glp_intfeas1/MiniSat. This
        model along with a brief instruction (pbn.pdf) and benchmark
        examples from <webpbn.com> encoded in GNU MathProg (*.dat) can
        be found in subdirectory examples/pbn/.

        The glpsol lp/mip solver was modified to bypass postprocessing
        of MathProg models if the solution reported is neither optimal
        nor feasible.

        A minor bug in examples/Makefile.am was fixed to correctly
        build glpk in a separate directory. Thanks to Marco Atzeri
        <address@hidden> for bug report and patch.

GLPK 4.46 (release date: Au 9, 2011)Edit

        The following new API routines were added:

        glp_read_cnfsat    read CNF-SAT problem data in DIMACS format
        glp_check_cnfsat   check for CNF-SAT problem instance
        glp_write_cnfsat   write CNF-SAT problem data in DIMACS format
        glp_minisat1       solve CNF-SAT problem instance with MiniSat

        The routine glp_minisat1 is a driver to MiniSat, a CNF-SAT
        solver developed by Niklas Een and Niklas Sorensson, Chalmers
        University of Technology, Sweden. This routine is similar to
        the routine glp_intopt, however, it is intended to solve a 0-1
        programming problem instance, which is the MIP translation of
        a CNF-SAT problem instance.

        Detailed description of these new API routines can be found in
        the document "CNF Satisfiability Problem", which is included in
        the distribution (see files doc/cnfsat.tex and doc/cnfsat.pdf).

        The following new glpsol command-line options were added:

        --cnf filename     read CNF-SAT problem instance in DIMACS
                           format from filename and translate it to MIP
        --wcnf filename    write CNF-SAT problem instance in DIMACS
                           format to filename
        --minisat          solve CNF-SAT problem instance with MiniSat
                           solver

        The zlib compression library (version 1.2.5) was ANSIfied,
        modified according to GLPK requirements and included in the
        distribution as an external software module. Thus, now this
        feature is platform independent.

        Some bugs were fixed in the SQL table driver. Thanks to Xypron
        <address@hidden>.

GLPK 4.45 (release date: Dec 05, 2010)Edit

        This is a bug-fix release.

        Several bugs/typos were fixed. Thanks to
        Xypron <xypron.glpk@gmx.de>,
        Robbie Morrison <robbie@actrix.co.nz>, and
        Ali Baharev <ali.baharev@gmail.com> for reports.

        Some glpk documents was re-formatted and merged into a single
        document. Now the glpk documentation consists of the following
        three main documents (all included in the distribution):

        GLPK: Reference Manual

        GLPK: Graph and Network Routines

        Modeling Language GNU MathProg: Language Reference

GLPK 4.44 (release date: Jun 03, 2010)Edit

        The following suffixes for variables and constraints were
        implemented in the MathProg language:

        .lb     (lower bound),
        .ub     (upper bound),
        .status (status in the solution),
        .val    (primal value), and
        .dual   (dual value).

        Thanks to Xypron <xypron.glpk@gmx.de> for draft implementation
        and testing.

        Now the MathProg language allows comment records (marked by
        '#' in the very first position) in CSV data files read with the
        table statements. Note that the comment records may appear only
        in the beginning of a CSV data file.

        The API routine glp_cpp to solve the Critical Path Problem was
        added and documented.

GLPK 4.43 (release date: Feb 20, 2010)Edit

        This is a maintainer release.

        `configure.ac' was changed to allow building the package under
        Mac OS and Darwin with ODBC support.
        Thanks to Xypron <xypron.glpk@gmx.de> for suggestions and Noli
        Sicad <nsicad@gmail.com> for testing.

        The SQL table driver was improved to process NULL data. Thanks
        to Xypron <xypron.glpk@gmx.de>.

        Some bugs were fixed in the LP/MIP preprocessor.

GLPK 4.42 (release date: Jan 13, 2010)Edit

        The following new API routines were added:

        glp_check_dup         check for duplicate elements in sparse
                              matrix
        glp_sort_matrix       sort elements of the constraint matrix
        glp_read_prob         read problem data in GLPK format
        glp_write_prob        write problem data in GLPK format
        glp_analyze_bound     analyze active bound of non-basic variable
        glp_analyze_coef      analyze objective coefficient at basic
                              variable
        glp_print_ranges      print sensitivity analysis report (this
                              routine replaces lpx_print_sens_bnds and
                              makes it deprecated)

        For description of these new routines and the GLPK LP/MIP
        format see a new edition of the reference manual included in
        the distribution. (Chapter "Graph and network API routines" was
        carried out from the main reference manual and included in the
        distribution as a separate document.)

        The following new command-line options were added to the stand-
        alone solver glpsol:
        --glp filename        read problem data in GLPK format
        --wglp filename       write problem data in GLPK format
        --ranges filename     print sensitivity analysis report (this
                              option replaces --bounds)

        Now all GLPK routines performing file I/O support special
        filenames "/dev/stdin", "/dev/stdout", and "/dev/stderr", which
        can be specified in the same way as regular filenames. This
        feature is plaform-independent.

GLPK 4.41 (release date: Dec 21, 2009)Edit

        The following new API routies were added:

        glp_transform_row     transform explicitly specified row
        glp_transform_col     transform explicitly specified column
        glp_prim_rtest        perform primal ratio test
        glp_dual_rtest        perform dual ratio test

        For description of these new routines see a new edition of the
        reference manual included in the distribution.

        The following API routines are deprecated: lpx_transform_row,
        lpx_transform_col, lpx_prim_ratio_test, lpx_dual_ratio_test.

        Some improvements were made in the MIP solver (glp_intopt).

        The SQL table driver used to read/write data in MathProg models
        was changed to allow multiple arguments separated by semicolon
        in SQL statements. Thanks to Xypron <xypron.glpk@gmx.de>.

        Two new options were added to the glpsol stand-alone solver:
        --seed value (to initialize the pseudo-random number generator
        used in MathProg models with specified value), and
        --ini filename (to use a basis previously saved with -w option
        as an initial basis on solving similar LP's).

        Two new MathProg example models were included. Thanks to
        Nigel Galloway <nigel_galloway@operamail.com> and Noli Sicad
        <nsicad@gmail.com> for contribution.

        Scripts to build GLPK with Microsoft Visual Studio 2010 for
        both 32-bit and 64-bit Windows were included. Thanks to Xypron
        <xypron.glpk@gmx.de> for contribution and testing.

GLPK 4.40 (release date: Nov 03, 2009)Edit

        The following new API routines were added:

        glp_del_vertices      remove vertices from graph
        glp_del_arc           remove arc from graph
        glp_wclique_exact     find maximum weight clique with the exact
                              algorithm developed by Prof. P. Ostergard
        glp_read_ccdata       read graph in DIMACS clique/coloring
                              format
        glp_write_ccdata      write graph in DIMACS clique/coloring
                              format

        For description of these new routines see a new edition of the
        reference manual included in the distribution.

        The hybrid pseudocost branching heuristic was included in the
        MIP solver. It is available on API level (iocp.br_tech should
        be set to GLP_BR_PCH) and in the stand-alone solver glpsol
        (via the command-line option --pcost). This heuristic may be
        useful on solving hard MIP instances.

        The branching heuristic by Driebeck and Tomlin (used in the
        MIP solver by default) was changed to switch to branching on
        most fractional variable if an lower bound of degradation of
        the objective is close to zero for all branching candidates.

        A bug was fixed in the LP preprocessor (routine npp_empty_col).
        Thanks to Stefan Vigerske <stefan@math.hu-berlin.de> for the
        bug report.

        A bug was fixed and some improvements were made in the FPUMP
        heuristic module. Thanks to Xypron <xypron.glpk@gmx.de>.

        A bug was fixed in the API routine glp_warm_up (dual
        feasibility test was incorrect in maximization case). Thanks to
        Uday Venkatadri <Uday.Venkatadri@dal.ca> for the bug report.

GLPK 4.39 (release date: Jul 26, 2009)Edit

        The following new API routines were added:

        glp_warm_up           "warm up" LP basis
        glp_set_vertex_name   assign (change) vertex name
        glp_create_v_index    create vertex name index
        glp_find_vertex       find vertex by its name
        glp_delete_v_index    delete vertex name index
        glp_read_asnprob      read assignment problem data in DIMACS
                              format
        glp_write_asnprob     write assignment problem data in DIMACS
                              format
        glp_check_asnprob     check correctness of assignment problem
                              data
        glp_asnprob_lp        convert assignment problem to LP
        glp_asnprob_okalg     solve assignment problem with the
                              out-of-kilter algorithm
        glp_asnprob_hall      find bipartite matching of maxumum
                              cardinality with Hall's algorithm

        Also were added some API routines to read plain data files.

        The API routines glp_read_lp and glp_write_lp to read/write
        files in CPLEX LP format were re-implemented. Now glp_write_lp
        correctly writes double-bounded (ranged) rows by introducing
        slack variables rather than by duplicating the rows.

        For description of these new routines see a new edition of the
        reference manual included in the distribution.

        The 'xfree(NULL)' bug was fixed in the AMD routines. Thanks to
        Niels Klitgord <niels@bu.edu> for bug report.

        The message "Crashing..." was changed to "Constructing initial
        basis..." due to suggestion by Thomas Kahle <tom111@gmx.de>.

        Some typos were corrected in glpsol output messages. Thanks to
        Xypron <xypron.glpk@gmx.de> for patch.

GLPK 4.38 (release date: May 02, 2009)Edit

        API routines glp_read_mps and glp_write_mps were improved.

        Some improvements were made in the dual simplex routines.

        Two external software modules AMD and COLAMD were included in
        the distribution (for more details please see src/amd/README
        and src/colamd/README). Now they are used in the interior-point
        solver to reorder the matrix prior to Cholesky factorization.

        API routine glp_ipt_status may return two new statuses due to
        changes in the routine glp_interior. For details please see the
        reference manual included in the distribution.

        A minor bug was fixed in the graph/network routines. Thanks to
        Nelson H. F. Beebe <beebe@math.utah.edu> for bug report.

GLPK 4.37 (release date: Mar 29, 2009)Edit

        The 0-1 Feasibility Pump heuristic was included in the GLPK
        integer optimizer glp_intopt. On API level the heuristic can be
        enabled by setting the parameter fp_heur in glp_iocp to GLP_ON.
        This feature is also available in the solver glpsol through
        command-line option '--fpump'. For more details please see the
        reference manual included in the distribution.

        The following new API routines were added:

        glp_print_sol         write basic solution in printable format
        glp_print_ipt         write interior-point solution in printable
                              format
        glp_print_mip         write MIP solution in printable format
        glp_read_graph        read (di)graph from plain text file
        glp_write_graph       write (di)graph to plain text file
        glp_weak_comp         find all weakly connected components
        glp_strong_comp       find all strongly connected components

        The following API routines are deprecated: lpx_print_sol,
        lpx_print_ips, lpx_print_mip, lpx_print_prob (the latter is
        equivalent to glp_write_lp).

        A bug was fixed in the interior-point solver (glp_interior) to
        correctly compute dual solution components when the problem is
        scaled.

        The files configure.ac and Makefile.am were changed:
        (a) to allow using autoreconf/autoheader;
        (b) to allow building the package in a directory other than its
            source directory.
        Thanks to Marco Atzeri <marco_atzeri@yahoo.it> for bug report.

        An example model in the GNU MathProg language was added.
        Thanks to Larry D'Agostino <Larry.D'Agostino@gmacrescap.com> for
        contribution.

GLPK 4.36 (release date: Feb 06, 2009)Edit

        The following new API routines were added to the package:

        glp_mincost_okalg     find minimum-cost flow with out-of-kilter
                              algorithm
        glp_maxflow_ffalg     find maximal flow with Ford-Fulkerson
                              algorithm

        For detailed description of these new routines and related data
        structures see chapter "Graph and Network API Routines" in a new
        edition of the reference manual included in the distribution.

        The following two new command-line options were added to the
        solver glpsol:

        --mincost             read min-cost flow data in DIMACS format
        --maxflow             read maximum flow data in DIMACS format

        Duplicate symbols in the header glpk.h were removed to allow
        using swig.
        Thanks to Kelly Westbrooks <kellywestbrooks@yahoo.com> and
        Nigel Galloway <nigel_galloway@operamail.com> for suggestion.

        A minor defect was fixed in the routine glp_write_lp.
        Thanks to Sebastien Briais <sbriais@free.fr> for bug report.

        A minor bug was fixed in the SQL module.
        Thanks to Xypron <xypron.glpk@gmx.de> for patch.

        Some new example models in the GNU MathProg modeling language
        were added. Thanks to Sebastian Nowozin <nowozin@gmail.com> and
        Nigel Galloway <nigel_galloway@operamail.com> for contribution.

GLPK 4.35 (release date: Jan 09, 2009)Edit

        The following new API routines were added to the package:

        glp_create_graph      create graph
        glp_set_graph_name    assign (change) graph name
        glp_add_vertices      add new vertices to graph
        glp_add_arc           add new arc to graph
        glp_erase_graph       erase graph content
        glp_delete_graph      delete graph
        glp_read_mincost      read minimum cost flow problem data in
                              DIMACS format
        glp_write_mincost     write minimum cost flow problem data in
                              DIMACS format
        glp_mincost_lp        convert minimum cost flow problem to LP
        glp_netgen            Klingman's network problem generator
        glp_gridgen           grid-like network problem generator
        glp_read_maxflow      read maximum flow problem data in DIMACS
                              format
        glp_write_maxflow     write maximum flow problem data in DIMACS
                              format
        glp_maxflow_lp        convert maximum flow problem to LP
        glp_rmfgen            Goldfarb's maximum flow problem generator

        For detailed description of these new routines and related data
        structures see chapter "Graph and Network API Routines" in a new
        edition of the reference manual included in the distribution.

        A minor change were made in the internal routine xputc. Thanks
        to Luiz Bettoni <bettoni@cpgei.ct.utfpr.edu.br> for suggestion.

        A minor bug was fixed in the internal routine mpl_fn_time2str.
        Thanks to Stefan Vigerske <stefan@vigerske.de> for bug report.

GLPK 4.34 (release date: Dec 04, 2008)Edit

        The GNU MathProg modeling language was supplemented with three
        new built-in functions:

        gmtime    obtaining current calendar time
        str2time  converting character string to calendar time
        time2str  converting calendar time to character string

        (Thanks to Xypron <xypron.glpk@gmx.de>.)

        For detailed description of these functions see Appendix A in
        the document "Modeling Language GNU MathProg", a new edition of
        which was included in the distribution.

        A bug was fixed in the MIP solver. Thanks to Nigel Galloway
        <nigel_galloway@operamail.com> for bug report.

        A new makefile was added to build the GLPK DLL with Microsoft
        Visual Studio Express 2008 for 64-bit Windows. Thanks to Xypron
        <xypron.glpk@gmx.de> for contribution and testing.

GLPK 4.33 (release date: Oct 30, 2008)Edit

        The following new API routines were added to the package:
        glp_copy_prob         copy problem object content
        glp_exact             solve LP in exact arithmetic
                              (makes lpx_exact deprecated)
        glp_get_unbnd_ray     determine variable causing unboundedness
                              (makes lpx_get_ray_info deprecated)
        glp_interior          solve LP with interior-point method
                              (makes lpx_interior deprecated)

        The following new API routines for processing models written in
        the GNU Mathprog language were added to the package:
        glp_mpl_alloc_wksp    allocate the translator workspace
        glp_mpl_read_model    read and translate model section
        glp_mpl_read_data     read and translate data section
        glp_mpl_generate      generate the model
        glp_mpl_build_prob    build LP/MIP instance from the model
        glp_mpl_postsolve     postsolve the model
        glp_mpl_free_wksp     deallocate the translator workspace
        (These routines make lpx_read_model deprecated.)

        For description of all these new API routines see the reference
        manual included in the distribution.

        A crude implementation of CPLEX-like interface to GLPK API was
        added to the package. Currently it allows using GLPK as a core
        LP solver for Concorde, a well known computer code for solving
        the symmetric TSP. For details see examples/cplex/README.

        Some bugs were fixed in the SQL table driver. Thanks to Xypron
        <xypron.glpk@gmx.de>.

GLPK 4.32 (release date: Oct 03, 2008)Edit

        The following new features were included in the MIP solver
        (the API routine glp_intopt):

        *  MIP presolver
        *  mixed cover cut generator
        *  clique cut generator
        *  Euclidean reduction of the objective value

        Due to changes the routine glp_intopt may additionally return
        GLP_ENOPFS, GLP_ENODFS, and GLP_EMIPGAP.

        The API routines lpx_integer are lpx_intopt are deprecated,
        since they are completely superseded by glp_intopt.

        The following new branch-and-cut API routines were added:
        glp_ios_row_attr      determine additional row attributes
        glp_ios_pool_size     determine current size of the cut pool
        glp_ios_add_row       add constraint to the cut pool
        glp_ios_del_row       delete constraint from the cut pool
        glp_ios_clear_pool    delete all constraints from the cut pool

        For description of these new routines see the reference manual
        included in the distribution.

        The stand-alone solver glpsol was changed to allow multiple
        data files.

        A new edition of the supplement "Using Data Tables in the GNU
        MathProg Modeling Language" was included.

        As usual, some bugs were fixed (in the MathProg translator).
        Thanks to Xypron <xypron.glpk@gmx.de>.

GLPK 4.31 (release date: Sep 02, 2008)Edit

        The core LP solver based on the dual simplex method was
        re-implemented and now it provides both phases I and II.

        The following new API routines were added:
        glp_scale_prob  automatic scaling of problem data
        glp_std_basis   construct standard initial LP basis
        glp_adv_basis   construct advanced initial LP basis
        glp_cpx_basis   construct Bixby's initial LP basis

        For description of these new routines see the reference manual
        included in the distribution.

        The following API routines are deprecated:
        lpx_scale_prob, lpx_std_basis, lpx_adv_basis, lpx_cpx_basis.

        Necessary changes were made in memory allocation routines to
        resolve portability issues for 64-bit platforms.

        New version of the routine lpx_write_pb to write problem data
        in OPB (pseudo boolean format) was added to the package. Thanks
        to Oscar Gustafsson <oscarg@isy.liu.se> for the contribution.

        Two new makefiles were added to build the package for 32- and
        64-bit Windows with Microsoft Visual Studio Express 2008.
        Thanks to Heinrich Schuchardt <heinrich.schuchardt@gmx.de> (aka
        Xypron) for the contribution and testing.

        Two new makefiles were added to build the package with Digital
        Mars C/C++ 8.50 and Open Watcom C/C++ 1.6 (for 32-bit Windows).

GLPK 4.30 (release date: Aug 13, 2008)Edit

        The core LP solver based on the primal simplex method was
        re-implemented to allow its further improvements. Currently the
        new version provides the same features as the old one, however,
        it is a bit faster and more numerically stable.

        Some changes were made in the MathProg translator to allow <,
        <=, >=, and > on comparing symbolic values. Thanks to Heinrich
        Schuchardt <heinrich.schuchardt@gmx.de> for patches.

        Internal routine set_d_eps in the exact LP solver was changed
        to prevent approximation errors in case of integral data.
        Thanks to Markus Pilz <pilz@cs.uni-bonn.de> for bug report.

GLPK 4.29 (release date: Jul 06, 2008)Edit

        The configure script was changed to disable all optional
        features by default. For details please see file INSTALL.

        The following new API routines were added:
        glp_erase_prob  erase problem object content
        glp_read_mps    read problem data in MPS format
        glp_write_mps   write problem data in MPS format
        glp_read_lp     read problem data in CPLEX LP format
        glp_write_lp    write problem data in CPLEX LP format

        For description of these new routines see the reference manual
        included in the distribution.

        The following API routines are deprecated:
        lpx_read_mps, lpx_read_freemps, lpx_write_mps,
        lpx_write_freemps, lpx_read_cpxlp, and lpx_write_cpxlp.

        Two bugs were fixed. Thanks to
        Anne-Laurence Putz <anne-laurence.putz@eurodecision.com> and
        Xypron <xypron.glpk@gmx.de> for bug report.

GLPK 4.28 (release date: Mar 25, 2008)Edit

        The iODBC and MySQL table drivers, which allows transmitting
        data between MathProg model objects and relational databases,
        were re-implemented to replace a static linking by a dynamic
        linking to corresponding shared libraries.
        Many thanks to Heinrich Schuchardt <heinrich.schuchardt@gmx.de>
        for the contribution, Rafael Laboissiere <rafael@debian.org>
        for useful advices concerning the shared library support under
        GNU/Linux, and Vijay Patil <vijay.patil@gmail.com> for testing
        this feature under Windows XP.

        A new optional feature was added to the package. This feature
        is based on the zlib data compression library and allows GLPK
        API routines and the stand-alone solver to read and write
        compressed data files performing compression/decompression "on
        the fly" (compressed data files are recognized by suffix `.gz'
        in the file name). It may be useful in case of large MPS files
        to save the disk space (up to ten times).

        The `configure' script was re-implemented. Now it supports the
        following specific options:

        --with-gmp           Enable using the GNU MP bignum library
        --without-gmp        Disable using the GNU MP bignum library
        --with-zlib          Enable using the zlib data compression
                             library
        --without-zlib       Disable using the zlib data compression
                             library
        --enable-dl          Enable shared library support (auto check)
        --enable-dl=ltdl     Enable shared library support (GNU)
        --enable-dl=dlfcn    Enable shared library support (POSIX)
        --disable-dl         Disable shared library support
        --enable-odbc        Enable using ODBC table driver
        --disable-odbc       Disable using ODBC table driver
        --enable-mysql       Enable using MySQL table driver
        --disable-mysql      Disable using MySQL table driver

        For more details please see file INSTALL.

GLPK 4.27 (release date: Mar 02, 2008)Edit

        Three new table drivers were added to the MathProg translator:

        xBASE built-in table driver, which allows reading and writing
        data in .dbf format (only C and N fields are supported);

        MySQL table driver, which provides connection to a MySQL
        database;

        iODBC table driver, which provides connection to a database
        through ODBC.

        The MySQL and iODBC table drivers were contributed to GLPK by
        Heinrich Schuchardt <heinrich.schuchardt@gmx.de>.

        The table driver is a program module which allows transmitting
        data between MathProg model objects and external data tables.

        For detailed description of the table statement and table
        drivers see the document "Using Data Tables in the GNU MathProg
        Modeling Language" (file doc/tables.txt) included in the
        distribution. Some examples which demonstrate using MySQL and
        iODBC table drivers can be found in subdirectory examples/sql.

GLPK 4.26 (release date: Feb 17, 2008)Edit

        The table statement was implemented in the GNU MathProg
        modeling language. This new feature allows reading data from
        external tables into model objects such as sets and parameters
        as well as writing results of computations to external tables.

        A table is a (unordered) set of records, where each record
        consists of the same number of fields, and each field is
        provided with a unique symbolic name called the field name.

        Currently the GLPK package has the only built-in table driver,
        which supports tables in the CSV (comma-separated values) file
        format. This format is very simple and supported by almost all
        spreadsheets and database management systems.

        Detailed description of the table statement and CSV format can
        be found in file doc/tables.txt, included in the distribution.

GLPK 4.25 (release date: Dec 19, 2007)Edit

        A tentative implementation of Gomory's mixed integer cuts was
        included in the branch-and-cut solver. To enable generating
        Gomory's cuts the control parameter gmi_cuts passed to the
        routine glp_intopt should be set to GLP_ON. This feature is
        also available in the solver glpsol through command-line option
        '--gomory'. For more details please see the reference manual
        included in the distribution.

GLPK 4.24 (release date: Nov 21, 2007)Edit

        A tentative implementation of MIR (mixed integer rounding) cuts
        was included in the MIP solver. To enable generating MIR cuts
        the control parameter mir_cuts passed to the routine glp_intopt
        should be set to GLP_ON. This feature is also available in the
        stand-alone solver glpsol via command-line option '--mir'. For
        more details please see the reference manual included in the
        distribution.

        The implementation is mainly based on the following two papers:

        1. H. Marchand and L. A. Wolsey. Aggregation and mixed integer
           rounding to solve MIPs. CORE discussion paper 9839, CORE,
           Universite catholique de Louvain, June 1998.

        2. G. Andreello, A. Caprara, and M. Fischetti. Embedding cuts
           in a Branch&Cut framework. Preliminary draft, October 2003.

        MIR cuts can be generated on any level of the search tree that
        makes the GLPK MIP solver to be a real branch-and-cut solver.

        A bug was fixed in the routine lpx_write_cpxlp. If a variable
        x has upper bound and no lower bound, it should appear in the
        bounds section as "-inf <= x <= u", not as "x <= u". Thanks to
        Enric Rodriguez <erodri@lsi.upc.edu> for the bug report.

GLPK 4.23 (release date: Oct 28, 2007)Edit

        The following new API routines were added:

        glp_read_sol    read basic solution from text file
        glp_write_sol   write basic solution to text file
        glp_read_ipt    read interior-point solution from text file
        glp_write_ipt   write interior-point solution to text file
        glp_read_mip    read MIP solution from text file
        glp_write_mip   write MIP solution to text file

        For description of these routines and corresponding file
        formats see Chapter "API Routines", Section "Utility routines"
        in the reference manual included in the distribution.

        Advanced API routine glp_free_env was added. It may be used by
        the application program to free all resources allocated by GLPK
        routines.

        The following three new command-line options were added to the
        solver glpsol:

        --mipgap tol    set relative MIP gap tolerance
        -r filename     read solution from filename
        -w filename     write solution to filename

GLPK 4.22 (release date: Sep 19, 2007)Edit

        This is a maintainer release.

        A bug was fixed in the MIP preprocessor (ios_preprocess_node).
        Thanks to Roberto Bagnara <bagnara@cs.unipr.it> (Department of
        Mathematics, University of Parma, Italy) for the bug report.

        A bug was fixed in the MIP preprocessor (col_implied_bounds),
        due to which constraint coefficients with small magnitude could
        lead to wrong implied bounds of structural variables.

        A similar bug was fixed in the routine reduce_bounds.

        A bug was fixed in the routines glp_set_mat_row and
        glp_set_mat_col. (The bug appeared due to incorrect removing
        zero elements from the row/column lists.)

        A bug was fixed in the API routines lpx_read_mps and
        lpx_read_freemps, due to which bounds of type LI specified in
        BOUNDS section were incorrectly processed.

        A call to standard function vsprintf was replaced by a call to
        vsnprintf for security reasons. Many thanks to Peter T. Breuer
        <ptb@inv.it.uc3m.es> and Rafael Laboissiere <rafael@debian.org>.

GLPK 4.21 (release date: Aug 28, 2007)Edit

        Additional reasons for calling the callback routine used in the
        MIP solver (glp_intopt) were introduced. Currently the following
        reasons are supported:

        * request for subproblem selection
        * request for preprocessing
        * request for row generation
        * request for heuristic solution
        * request for cut generation
        * request for branching
        * better integer solution found

        A basic preprocessing component used to improve subproblem
        formulations by tightening bounds of variables was included in
        the MIP solver. Depending on the control parameter pp_tech
        passed to the routine glp_intopt the preprocessing can be
        performed either on the root level or on all levels (default)
        or can be disabled.

        Backtracking heuristic used by default in the MIP solver was
        changed to the "best local bound".

        For more details see Chapter "Advanced API routines", Section
        "Branch-and-bound interface routines" in a new edition of the
        reference manual included in the distribution.

GLPK 4.20 (release date: Jul 26, 2007)Edit

        API routine lpx_integer was replaced by API routine glp_intopt,
        which provides equivalent functionality and additionally allows
        the application to control the solution process by means of the
        user-written callback routine, which is called by the solver at
        various points of the branch-and-bound algorithm. Besides, the
        new MIP solver allows generating "lazy" constraints and cutting
        planes on all levels of the branch-and-bound tree, not only on
        the root level. The routine lpx_integer is also still available
        for the backward compatibility.

        The following new advanced API routines, which may be called
        from the B&B callback routine, were included in the package:

        glp_ios_reason     determine reason for calling callback
                           routine
        glp_ios_get_prob   access the problem object
        glp_ios_tree_size  determine size of the branch-and-bound tree
        glp_ios_curr_node  determine current active subproblem
        glp_ios_next_node  determine next active subproblem
        glp_ios_prev_node  determine previous active subproblem
        glp_ios_up_node    determine parent subproblem
        glp_ios_node_level determine subproblem level
        glp_ios_node_bound determine subproblem local bound
        glp_ios_mip_gap    compute relative MIP gap
        glp_ios_heur_sol   provide solution found by heuristic
        glp_ios_terminate  terminate the solution process

        For description of these routines see Chapter "Advanced API
        routines", Section "Branch-and-bound interface routines" in a
        new edition of the reference manual, which was included in the
        distribution.

        Old version of the integer optimization suite (IOS) as well as
        TSP solver tspsol based on it are no longer supported and were
        removed from the package.

        A minor error in the MIP presolver was fixed; thanks to Graham
        Rockwell <bionomicron@gmail.com> for the bug report.

GLPK 4.19 (release date: Jul 05, 2007)Edit

        The principal change is upgrading to GPLv3.

        A serious bug in the routine glp_del_cols was fixed; thanks to
        Cedric[FR] <fox2113@wanadoo.fr> for the bug report. The bug
        appeared because on deleting non-basic columns the basis header
        remained valid, however, contained invalid (old) column ordinal
        numbers.

        A new advanced API routine glp_mem_limit was added.

        The case GLP_EBOUND was added to the routine lpx_simplex.
        Thanks to Cameron Kellough <Cameron.Kellough@sri.com> for the
        bug report.

        An API routine lpx_write_pb to write the problem instance in
        OPB (pseudo boolean) format format was added. Thanks to Oscar
        Gustafsson <oscarg@isy.liu.se> for the contribution.

        Two new options --wpb and --wnpb were added to glpsol to write
        the problem instance in OPB format.

GLPK 4.18 (release date: Jun 25, 2007)Edit

        The following new API routines were added:

        glp_set_rii        set (change) row scale factor
        glp_set_sjj        set (change) column scale factor
        glp_get_rii        retrieve row scale factor
        glp_get_sjj        retrieve column scale factor
        glp_simplex        solve LP problem with the simplex method
                           (this routine replaces lpx_simplex, which is
                           also available for backward compatibility)
        glp_init_smcp      initialize simplex method control params
        glp_bf_exists      check if the basis factorization exists
        glp_factorize      compute the basis factorization
        glp_bf_updated     check if the basis factorization has been
                           updated
        glp_get_bfcp       retrieve basis factorization control params
        glp_set_bfcp       change basis factorization control params
        glp_get_bhead      retrieve the basis header information
        glp_get_row_bind   retrieve row index in the basis header
        glp_get_col_bind   retrieve column index in the basis header
        glp_ftran          perform forward transformation
        glp_btran          perform backward transformation

        For description of all these routines see a new edition of the
        reference manual included in the distribution.

        Type names ulong_t and uldiv_t were changed to glp_ulong and
        glp_uldiv to avoid conflicts with standard type names on some
        platforms. Thanks to Boris Wirtz <Boris.Wirtz@uni-oldenburg.de>
        for the bug report.

        Some new examples in the MathProg language were added. Thanks
        to Sebastian Nowozin <nowozin@gmail.com>.

GLPK 4.17 (release date: May 26, 2007)Edit

        API routines glp_set_mat_row, glp_set_mat_col, and glp_load_mat
        were modified to allow zero constraint coefficients (which are
        not stored in the constraint matrix). Note that constraint
        coefficients with duplicate row/column indices are not allowed.

        Another form of LP basis factorization was implemented in the
        package. It is based on LU-factorization of an initial basis
        and Schur complement to reflect changes in the basis. Currently
        the implementation is incomplete and provides only updating the
        factorization on replacing a column of the basis matrix. On API
        level the user can set the control parameter LPX_K_BFTYPE to
        choose between the folloiwng forms of LP basis factorization to
        be used in the simplex method routines:
        1) LU + Forrest-Tomlin update;
        2) LU + Schur complement + Bartels-Golub update;
        3) LU + Schur complement + Givens rotation update.
        The GLPK implementation is similar to LUSOL/LUMOD developed by
        Michael A. Saunders.

        The user can choose the form of LP basis factorzation used by
        the simplex method routines by specifying the folloiwng options
        of glpsol: --luf, --cbg, --cgr.

GLPK 4.16 (release date: May 05, 2007)Edit

        A number of basic GLPK API routines, which now are in the
        stable stable, were renamed to be prefixed with 'glp_'. Note
        that all these routines are available via their old names
        prefixed with 'lpx_' that keeps the downward compatibility with
        older versions of the package.

        Three new GLPK API routines were added to the package:
        glp_version, glp_term_hook, and glp_mem_usage; for more details
        see a new edition of the GLPK reference manual included in the
        distribution. The routine glp_version reports the actual version
        of the GLPK library and also can be used (along with the header
        glpk.h) in Autotools specification files to check if the GLPK
        library has been installed.

        The header glpk.h was changed to conform to C++ environment.

GLPK 4.15 (release date: Feb 18, 2007)Edit

        Autotools specification files (configure.ac, Makefile.am) were
        changed to use GNU Libtool. This allows building the static as
        well as shared GLPK library.

GLPK 4.14 (release date: Feb 05, 2007)Edit

        Now GLPK conforms to ILP32, LLP64, and LP64 programming models
        (the latter seems to be the ultimate choice regarding 64-bit
        architectures). Note that GLPK itself is a 32-bit application,
        and the conformity only means that the package works correctly
        on all these arenae. Nevertheless, on 64-bit platforms it is
        possible to use more than 4GB of memory, if necessary.

GLPK 4.13 (release date: Nov 13, 2006)Edit

        A tentative implementation of the "exact" simplex method based
        on bignum (rational) arithmetic was included in the package.

        On API level this new feature is available through the routine
        lpx_exact, which is similar to the routine lpx_simplex.

        In the solver glpsol this feature is available through two new
        command-line options: --exact and --xcheck. If the '--exact'
        option is specified, glpsol solves LP instance using the exact
        simplex method; in case of MIP it is used to obtain optimal
        solution of LP relaxation. If the --xcheck option is specified,
        LP instance (or LP relaxation) is solved using the standard
        (floating-point) simplex method, however, then glpsol calls the
        exact simplex routine to make sure that the final LP basis is
        exactly optimal, and if it is not, to perform some additional
        simplex iterations in exact arithmetic.

GLPK 4.12 (release date: Nov 08, 2006)Edit

        A tentative implementation of some simplex method routines
        based on exact (bignum) arithmetic was included in the package.
        Currently these routines provide computing LU-factorization of
        the basis matrix and computing components of basic solution.

        These routines were used to implement a routine, which checks
        primal and dual feasibility of basic solution exactly, i.e. in
        rational numbers, without round-off errors. In glpsol this
        feature is available through the command-line option --xcheck.

        GLPK has its own low-level routines implementing operations on
        integer and rational numbers that makes it independent on other
        software packages. However, to attain a much better performance
        it is highly recommended to install (before configuring GLPK)
        the GNU Multiple Precision Arithmetic Library (GMP). Using GMP
        makes computations 100-200 times faster.

GLPK 4.11 (release date: Jul 25, 2006)Edit

        Three new built-in functions in the modeling language were
        implemented: card (cardinality of set), length (length of
        character string), and substr (substring of character string).
        Another improvement concerns the printf statement which now
        allows redirecting its output to a specified file. These new
        features are illustrated in example models crypto.mod and
        graph.mod included in the distribution. For more details see
        the document "Modeling Language GNU MathProg".

        Four batch files (along with corresponding makefiles) were
        included in the distribution to simplify building GLPK under
        MS Windows; see them in subdirectory 'w32'.

GLPK 4.10 (release date: May 11, 2006)Edit

        Cutting planes of two new classes were implemented: mixed cover
        cuts and clique cuts. On API level this feature can be enabled
        by setting control parameter LPX_K_USECUTS passed to the routine
        lpx_intopt. In glpsol this feature is available through the
        command-line options --cover and --clique. For more details see
        the reference manual.

        Now the routines lpx_read_mps and lpx_read_freemps support LI
        bound type. It is similar to LO, however, indicates the column
        as of integer kind.

GLPK 4.9 (release date: Jan 17, 2006)Edit

        An advanced MIP solver was implemented. It includes:

        - basic presolving technique (removing free, singleton and
          redundant rows, improving bounds of columns, removing fixed
          columns, reducing constraint coefficents);

        - generating cutting planes to improve LP relaxation (currently
          only Gomory's mixed integer cuts are implemented);

        - using the branch-and-bound method to solve resultant MIP;

        - recovering solution of the original MIP.

        The solver is available on API level via the routine lpx_intopt
        (see the reference manual). It is similar to the routine
        lpx_integer, however, does not require initial solution of LP
        relaxation.

        The solver is also available in the command-line utility glpsol
        via two options: --intopt (only presolving) and --cuts (assumes
        --intopt plus generating cuts).

        Note that efficiency of the MIP solver strongly depends on the
        internal structure of the problem to be solved. For some hard
        instances it is very efficient, but for other instances it may
        be significantly worse than the standard branch-and-bound.

        For some comparative benchmarks see doc/bench1.txt.

        Well, what else...

        Three built-in functions were added to MathProg: sin, cos, and
        atan (the latter allows one or two arguments).

        Some bugs were fixed.

        Several new examples in MathProg were included: color.mod
        (graph coloring problem), tsp.mod (traveling salesman problem),
        and pbn.mod (paint-by-numbers puzzle).

GLPK 4.8 (release date: Jan 12, 2005)Edit

        Core simplex method and interior-point method routines were
        re-implemented and now they use a new, "storage-by-rows" sparse
        matrix format (unlike previous versions where linked lists were
        used to represent sparse matrices). For details see ChangeLog.

        Also a minor bug was fixed in API routine lpx_read_cpxlp.

GLPK 4.7 (release date: Aug 23, 2004)Edit

        Now GLPK supports free MPS format. Two new API routines
        lpx_read_freemps (to read problem data in free MPS format) and
        lpx_write_freemps (to write problem data in free MPS format)
        were added. This feature is also available in the solver glpsol
        via new command-line options --freemps and --wfreemps. For more
        details see the GLPK reference manual.

        API routines lpx_read_cpxlp and lpx_write_cpxlp for reading and
        writing problem data in CPLEX LP format were re-implemented to
        allow long symbolic names (up to 255 characters).

        The following three modules were temporarily removed from the
        GLPK distribution due to licensing problems: DELI (an interface
        module to Delphi), GLPKMEX (an interface module to Matlab), and
        JNI (an interface module to Java).

GLPK 4.6 (release date: Aug 04, 2004)Edit

        Three new statements were implemented in the GNU MathProg
        language: solve, printf, and for. Their detailed description can
        be found in the GLPK documentation included in the distribution.
        (See also a sample model, examples/queens.mod, which illustrates
        using these new statements.)

        Two new API routines were added to the package: lpx_read_prob
        and lpx_write_prob. They allow reading/writing problem data in
        GNU LP low-level text format.

        Three new command-line options were implemented in the LP/MIP
        solver glpsol: --glp (to read problem data in GNU LP format),
        --wglp (to write problem data in GNU LP format), and --name (to
        change problem name). Now glpsol also supports processing models
        where the new statements (see above) are used.

        A new version of GLPKMEX, a Matlab MEX interface to GLPK, was
        included. For more details see contrib/glpkmex/ChangeLog.

GLPK 4.5 (release date: Jul 19, 2004)Edit

        The branch-and-bound solver was completely re-implemented.

        Some modifications were made in memory allocation routines that
        allows using the package on 64-bit platforms.

        For more details see ChangeLog.

GLPK 4.4 (release date: Jan 17, 2004)Edit

        All API routines were re-implemented using new data structures.
        The new implementation provides the same specifications and
        functionality of API routines as the old one, however, it has
        some important advantages, in particular:
        * linked lists are used everywhere that allows creating and
          modifying the problem object as efficiently as possible
        * all data stored in the problem object are non-scaled (even if
          the internal scaling is used) that prevents distortion of the
          original problem data
        * solution components obtained by the solver remain available
          even if the problem object has been modified
        * no solver-specific data are used in the new data structures
          that allows attaching any external lp/mip solver using GLPK
          API as an uniform interface
        Note that some API routines became obsolete being replaced by
        new, more convenient routines. These obsolete routines are kept
        for backward compatibility, however, they will be removed in
        the future. For more details please see ChangeLog and the GLPK
        Reference Manual.

        New edition of the GLPK Reference Manual was included in the
        distribution.

        GLPKMEX, a Matlab MEX interface to GLPK package, contributed by
        Nicolo Giorgetti <giorgetti@dii.unisi.it> was included in the
        distribution.

        GLPK FAQ contributed by Harley Mackenzie <hjm@bigpond.com> was
        included in the distribution.

GLPK 4.3 (release date: Dec 12, 2003)Edit

        The bug, due to which the standard math library is not linked
        on building the package on some platforms, was fixed.

        The following new built-in functions were added to the MathProg
        language: round, trunc, Irand224, Uniform01, Uniform, Normal01,
        Normal. For details see the language description.

        The MathProg syntax was changed to allow writing 'subj to' that
        means 'subject to'.

        The new api routine lpx_get_ray_info was added. It is intended
        to determine which (non-basic) variable causes unboundness. For
        details see the reference manual.

        The module glpmps.c was changed to avoid compilation errors on
        building the package on Mac OS X.

        Several typos was fixed and some new material was added to the
        GLPK documentation.

GLPK 4.2 (release date: Nov 14, 2003)Edit

        A preliminary implementation of the Integer Optimization Suite
        (IOS) was included in the package. The Branch-and-Cut Framework
        being completely superseded by IOS was removed from the package.

        New API routine lpx_print_sens_bnds intended for bounds
        sensitivity analysis was contributed to GLPK by Brady Hunsaker
        <hunsaker@engr.pitt.edu>. This function is also available in
        the solver glpsol (via command-line option --bounds).

        An improved version of GLPK JNI (Java Native Interface) was
        contributed by Chris Rosebrugh <cpr@pobox.com>.

        GLPK DELI (Delphi Interface) was contributed by Ivo van Baren
        <i.van.baren@freeler.nl>.

        Several makefiles were added to allow compiling GLPK on some
        non-GNU 32-bit platforms:
        * Windows single-threaded static library, Visual C++ 6.0
        * Windows multi-threaded dynamic library, Visual C++ 6.0
        * Windows single-threaded static library, Borland C++ 5.2
        * DOS single-threaded static library, Digital Mars C++ 7.50

        And, of course, some bugs were fixed.

        For more details see ChangeLog.

GLPK 4.1 (release date: Aug 23, 2003)Edit

        Some improvements were made in the lp/mip solver routines and
        several bugs were fixed in the model translator.

        For more details see ChangeLog.

GLPK 4.0 (release date: May 06, 2003)Edit

        Now GLPK supports the GNU MathProg modeling language, which is
        a subset of the AMPL modeling language.

        The document "GLPK: Modeling Language GNU MathProg" included in
        the distribution is a complete description of GNU MathProg. (See
        the files lang.latex, lang.dvi, and lang.ps in the subdirectory
        'doc'. See also some examples in the subdirectory 'sample'.)

        New version of the solver glpsol, which supports models written
        in GNU MathProg, was implemented. (Brief instructions how to use
        glpsol can be found in the GNU MathProg documentation.)

        The GLPK/L modeling language is no more supported. The reason is
        that GNU MathProg being much more powerful completely supersedes
        all features of GLPK/L.

GLPK 3.3 (release date: Mar 25, 2003)Edit

        LP PRESOLVER
        ------------

        Now the routine lpx_simplex (which is a driver to the simplex
        method for solving LP) is provided with the built-in LP
        presolver, which is a program that transforms the original LP
        problem to an equivalent LP problem, which may be easier for
        solving with the simplex method than the original one. Once the
        transformed LP has been solver, the presolver transforms its
        basic solution back to a corresponding basic solution of the
        original problem. For details about this feature please see the
        GLPK reference manual.

        Currently the LP presolver implements the following features:
        * removing empty rows;
        * removing empty columns;
        * removing free rows;
        * removing fixed columns;
        * removing row singletons, which have the form of equations;
        * removing row singletons, which have the form of inequalities;
        * removing column singletons, which are implied slack variables;
        * fixing and removing column singletons, which are implied free
          variables;
        * removing forcing rows that involves fixing and removing the
          corresponding columns;
        * checking for primal and dual infeasibilities.

        The LP presolver is also used by default in the stand-alone
        program glpsol. In order *not* to use it, the option --nopresol
        should be specified in the command-line.

        CHANGES IN GLPK/L
        -----------------

        The syntax and semantics of the GLPK/L modeling language was
        changed to allow declaration of "interval" sets. This means that
        now the user can declare a set, for example, as:

           set task = [8:11];

        that is exactly equivalent to the following declaration:

           set task = (task_8, task_9, task_10, task_11);

        For details see the language description.

        JAVA INTERFACE
        --------------

        Now GLPK includes the package GLPK JNI (Java Native Interface)
        that implements Java binding for GLPK. It allows Java programs
        to utilize GLPK in solving LP and MIP problems. For details see
        a brief user's guide in the subdirectory contrib/java-binding.
        This package was developed and programmed by Yuri Victorovich
        <yuri@gjt.org>, who contributed it to GLPK.

GLPK 3.2.4 (release date: Feb 18, 2003)Edit

        This is a bug-fix release. For details see ChangeLog.

GLPK 3.2.3 (release date: Nov 11, 2002)Edit

        A new implementation of the api routine lpx_integer which now
        is based on the b&b driver (which is based on the implicit
        enumeration suite) was included in the package. This new
        implementation has exactly the same functionality as the old
        version, so all changes are transparent to the api user.

        Four new api routines were included in the package:
        lpx_check_kkt checks Karush-Kuhn-Tucker optmality conditions;
        lpx_read_bas reads predifined basis in MPS format;
        lpx_write_bas writes current basis in MPS format;
        lpx_write_lpt writes problem data in CPLEX LP format.

        Also other minor improvements were made (for details see the
        file 'ChangeLog').

GLPK 3.2.2 (release date: Oct 14, 2002)Edit

        The api routine lpx_read_lpt was included in the package. It
        is similar to the routine lpx_read_mps and intended to read
        LP/MIP data prepared in CPLEX LP format. Description of this
        format is given in the GLPK reference manual, a new edition of
        which was also included in the distribution (see the files
        'refman.latex', 'refman.dvi', 'refman.ps' in the subdirectory
        'doc'). In order to use data files in CPLEX LP format with the
        solver glpsol the option '--lpt' should be specified in the
        command line.

        Several bugs were fixed and some minor improvements were made
        (for details see the file 'ChangeLog').

GLPK 3.2.1 (release date: Aug 12, 2002)Edit

        Now GLPK includes a preliminary implementation of the
        branch-and-cut framework, which is a set of data structures and
        routines intended for developing branch-and-cut methods for
        solving mixed-integer and combinatorial optimization problems.

        Detailed decsription of the branch-and-cut framework is given in
        the document "GLPK: A Preliminary Implementation of the
        Branch-And-Cut Framework" included in the distribution (see the
        file 'brcut.txt' in the subdirectory 'doc').

        In order to illustrate how the GLPK branch-and-cut framework
        can be used for solving a particular optimization problem there
        is an example included in the package. This is a stand-alone
        program, TSPSOL, which is intended for solving to optimality the
        symmetric Traveling Salesman Problem (TSP), a classical problem
        of the combinatorial optimization (see the file 'tspsol.c' in
        the subdirectory 'sample').

GLPK 3.2 (release date: Jul 15, 2002)Edit

        New edition of the document "GLPK: Reference Manual" was
        included (see the files 'refman.latex', 'refman.dvi', and
        'refman.ps' in the subdirectory 'doc').

        New edition of the document "GLPK: Modeling Language GLPK/L" was
        included (see the files 'lang.latex', 'lang.dvi', and 'lang.ps'
        in the subdirectory 'doc').

        The following new API routines were added to the package:

        lpx_transform_row (transform explicitly specified row);
        lpx_transform_col (transform explicitly specified column);
        lpx_prim_ratio_test (perform primal ratio test);
        lpx_dual_ratio_test (perform dual ratio test);
        lpx_interior (solve LP problem using interior point method);
        lpx_get_ips_stat (query status of interior point solution);
        lpx_get_ips_row (obtain row interior point solution);
        lpx_get_ips_col (obtain column interior point solution);
        lpx_get_ips_obj (obtain interior point value of obj.func.);
        lpx_read_lpm (read LP/MIP model written in GLPK/L);
        lpx_write_mps (write problem data using MPS format);
        lpx_print_ips (print interior point solution).

        Detailed description of all these new API routines are given in
        the new edition of the reference manual.

        New version of the stand-alone solver glpsol (which is based on
        the new API) was implemented.

        So long as the new API (introduced in glpk 3.0) now provides
        all the functions, which were provided by the old API, the old
        API routines were removed from the package at all.

GLPK 3.1 (release date: May 27, 2002)Edit

        A preliminary implementation of new API routines was completed
        and included in the package.

        These new API routines provide much more flexible interaction
        between the application program, LP/MIP problem instances, and
        solver routines. Based on completely changed data structures
        they are, however, similar to the API routines and provide the
        same functionality. Please note that three routines, namely,
        solving LPs using interior point method, reading model written
        in the GLPK/L modeling language, and writing problem data in
        the MPS format, are not implemented in the new API, however,
        these routines are planned to be implemented in the next version
        of the package.

        A description of the new API routines is given in the document
        "GLPK Reference Manual", a draft edition of which is included
        in the package (see the files 'refman.latex', 'refman.dvi', and
        'refman.ps' in the subdirectory 'doc').

        Although the old API routines are kept in the package, they are
        no longer supported and will be removed in the future.

GLPK 3.0.8 (release date: May 13, 2002)Edit

        A preliminary implementation of new API routines was included
        in the package. These new API routines are intended to provide
        much more flexible interaction between the application program,
        LP/MIP problem and solver routines. See the document "New GLPK
        API Routines" (the file 'newapi.txt' in the subdirectory 'doc')
        also included in the package.

        The api routines glp_simplex2, glp_call_ipm1, glp_call_bbm1 were
        renamed, respectively, to glp_simplex, glp_interior, glp_integer
        in order to reflect changes in implementation. The api routines
        glp_call_rsm1, glp_simplex1, glp_pivot_in, glp_pivout_out were
        removed from the package since they are completely supreseded by
        the new API routines (however, these routines still can be found
        in the subdirectory 'oldsrc'). Please consult a new edition of
        the document "GLPK User's Guide" about all these changes in the
        existing api routines.

        The document "GLPK Library Reference" was removed from the
        package (into the subdirectory 'oldsrc') since it describes the
        obsolete library routines, most of which are no longer used.

GLPK 3.0.7 (release date: Apr 22, 2002)Edit

        A new, more efficient implementation of the primal/dual simplex
        method was included in the package. Due to some improvements the
        simplex-based solver allows solving many LP problems faster and
        provides more reliable results. Note that the new implementation
        is currently incomplete and available only via the api routine
        glp_simplex2.

        All the changes are transparent on API level.

GLPK 3.0.6 (release date: Mar 28, 2002)Edit

        New version of LU-factorization and basis maintenance routines
        (based on Forrest-Tomlin updating technique) was implemented.
        Since these new routines functionally supersede some routines
        (which implement other forms of the basis matrix) and make them
        obsolete, the latter were removed from the package (they still
        can be found in the subdirectory 'oldsrc').

        All the changes are transparent on API level.

GLPK 3.0.5 (release date: Jan 29, 2002)Edit

        New edition of the document "GLPK User's Guide" was included in
        the distribution. Now it describes all additional API routines,
        which were recently added to the package.

        Structure of the package was re-organized in order to make its
        maintenance easier (all small files in the subdurectory 'source'
        were merged in bigger units). These changes are transparent for
        the user.

GLPK 3.0.4 (release date: Dec 10, 2001)Edit

        A new, more efficient implementation of the two-phase primal
        simplex method was included in the package. Due to some new
        features (an advanced initial basis, projected steepest edge,
        recursive updating values and reduced costs) the new LP solver
        is faster and numerically more stable than the old one.

        The new LP solver is available as API routine glp_simplex2 and
        has the same purpose as API routine glp_call_rsm1. For detailed
        specification see the file 'newapi.txt' in the directory 'doc'.

        Now the new LP solver is also used by default to solve an
        initial LP problem in the branch-and-bound routine glp_call_bbm1
        instead the routine rsm1_driver. Note that the branch-and-bound
        procedure itself is still based on rsm1_driver.

        The new LP solver is also used as default solver in GLPSOL for
        solving LP and MIP problems. In order to choose the old solver
        the option '--old-sim' can be specified in the command line.

GLPK 3.0.3 (release date: Oct 03, 2001)Edit

        Some minor changes were made in the simplex method routines in
        order to improve numerical stability of the method.

GLPK 3.0.2 (release date: Sep 24, 2001)Edit

        A new implementation of the basis maintaining routines was
        included in the package. These routines, which are based on so
        called FHV-factorization (a variety of LU-factorization) of the
        basis matrix and Gustavson's data structures, allows performing
        the main operations faster at the expense of some worsening
        numerical accuracy.

        AFI (Advanced Form of the Inverse), which is the form of the
        basis matrix based on FHV-factorization, is available via the
        parameter form = 3 (on API level) or via the option --afi (in
        GLPSOL solver).

GLPK 3.0.1 (release date: Aug 01, 2001)Edit

        Old GLPK API routines have been removed from the package.

        New GLPK API routines were added:

        - scaling routines;

        - a routine for writing problem data in MPS format;

        - a comprehensive driver to the simplex method;

        - basis maintaining routines.

        A description of the new API routines is given in the document
        "Additional GLPK API Routines". This document is included into
        the distribution in plain text format (see the file 'newapi.txt'
        in the subdirectory 'doc').

        Now the distribution includes a non-trivial example of using
        GLPK as a base LP solver for Concorde, a well known program that
        solves Traveling Salesman Problem (TSP). For further details see
        comments in the file 'sample/lpglpk30.c'.

GLPK 3.0 (release date: Jul 19, 2001)Edit

        Now GLPK is provided with new API, which being more flexible
        can be used in more complex algorithmic schemes.

        New edition of the document "GLPK User's Guide" is included in
        the distribution. Now it completely corresponds to the new GLPK
        API routines.

        Old API routines are not removed yet from the package, however
        they became obsolete and therefore should not be used. Since now
        the header glpk.h corresponds to new API, in order to compile
        existing programs that use old GLPK API routines the statement

        #define GLP_OLD_API

        should be inserted before the statement

        #include "glpk.h"

GLPK 2.4.1 (release date: Jun 14, 2001)Edit

        The document "Modeling language GLPK/L" is included into the
        distribution in texinfo format.

        New edition of the document "GLPK User's Guide" is included in
        the distribution. Now it describes all additional API routines
        which were recently added to the package.

GLPK 2.4 (release date: May 10, 2001)Edit

        Now GLPK includes an implementation of a preliminary version
        of the GLPK/L modeling language. This language is intended for
        writing mathematcal programming models. The name GLPK/L is
        derived from GNU Linear Programming Kit Language.

        A brief description of the GLPK/L language is given in the
        document "GLPK/L Modeling Language: A Brief Description". This
        document is included into the distribution in plain text format
        (see the file 'language.txt' in the subdirectory 'doc').

        The language processor (which is a program that analyzes model
        description written in GLPK/L and translates it to internal data
        structures) is available as the GLPK API routine.

        The stand-alone solver GLPSOL now is able: a) to process model
        descriptions written in the GLPK/L language; b) to solve pure LP
        problems using the interior point method (therefore the program
        GLPIPM was removed from the package).

GLPK 2.3 (release date: Apr 09, 2001)Edit

        New edition of the document "GLPK User's Guide" is included in
        the distribution. Now it describes all additional API routines
        which were recently added to the package.

        The MIP solver was fully re-programmed in order to improve its
        robustness and performance. In particular, a basis recovering
        procedure was implemented (this procedure allows switching to
        the primal simplex method in case when the dual simplex method
        fails).

GLPK 2.2 (release date: Mar 15, 2001)Edit

        Now GLPK includes a tentative implementation of the
        branch-and-bound procedure based on the dual simplex method for
        mixed integer linear programming (MIP).

        Complete description of this new feature of the package is given
        in the preliminary document "Mixed Integer Linear Programming
        Using GLPK Version 2.2 (Supplement to GLPK User's Guide)". This
        document is included into the distribution in plain text format
        (see the file 'mip.txt' in the subdirectory 'doc').

        The MIP solver (glp_integer) can be used as GLPK API routine in
        the same way as the pure LP solver (glp_simplex).

        The stand-alone program 'glpsol' is now able to solve LP as well
        as MIP problems.

        Note that the current version of GLPK MIP solver is based on
        easiest heuristics for branching and backtrackng. Therefore the
        solver is fit mainly for MIP problems which are not very hard
        and have few integer variables.

GLPK 2.1 (release date: Feb 19, 2001)Edit

        The document "GLPK Implementation of the Revised Simplex Method"
        is included into the distribution. This document describes most
        of routines related to the revised simplex method.

GLPK 2.0 (release date: Jan 25, 2001)Edit

        Now GLPK includes a tentative implementation of the primal-dual
        interior point method for large-scale linear programming.

        The interior point solver can be used as GLPK API routine in the
        same manner as the simplex method solver (glp_simplex):

        ret = glp_interior();

        Note that currently the interior point solver implemented in
        GLPK doesn't include many important features, in particular:

        * it can't process dense columns; therefore if the problem has
          dense columns, the solving will be extremely inefficient;

        * it has no special features against numerical unstability;
          some problems may cause premature termination of the solving
          when the matrix A*D*A' becomes ill-conditioned;

        * it computes only values of primal (auxiliary and structural)
          variables and doesn't compute values of dual variables (i.e.
          reduced costs) which are just set to zero;

        * it doesn't identify optimal basis corresponding to the found
          interior point solution; all variables in the found solution
          are just marked as basic variables.

        GLPK also includes a stand-alone program 'glpipm' which is a
        demo based on the interior point method. It may be used in the
        same way as the program 'glpsol' that is based on the simplex
        method.