GLPK 4.13 (release date: Nov 13, 2006)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

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

GLPK 3.2.3 (release date: Nov 11, 2002)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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)

        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.
