51 Distribution

Table of Contents

51.1.0 Major release (September 13, 2025)

Attention
This and forthcoming GAMS versions require a license in the new 8 lines format. License files with less than 8 lines are not accepted by the GAMS system anymore. A GAMS distributor or sales@gams.com can provide a new license file free of charge to eligible users.

Acknowledgments

We would like to thank all of our users who have reported problems and made suggestions for improving this release. In particular, we thank Miloš Bogataj, Bruce McCarl, Scott McDonald, and Uwe Schneider.

Platforms

  • We plan to drop support for Windows 10 with the next major release.
  • We plan to drop support for macOS 13 with the next major release.

GAMS System

GAMS

  • As announced, the use of =C= equations triggers an error now. For now, this can be turned into a warning, but with an upcoming major release, this will not be possible anymore. In case of concerns, contact support@gams.com.
  • Extended the dollar control options $show, $showMacros, and $showVariables to support an optional suffix .sorted. If that is used, the list of compile-time variables and/or macros is printed in alphabetical order.
  • Improved the dollar control options $show, $showFiles, $showMacros, and $showVariables to add a message to the log which can be clicked in GAMS Studio to jump to the right place in the .lst file.
  • The handling of the process directory (procDir) after a failed GAMS run has been refined. Previously, this directory was intentionally not deleted in certain error scenarios to preserve diagnostic information. However, in some cases (like a license error), this directory would be empty. With this release, GAMS will now correctly identify and delete these empty procDir folders to ensure better cleanup.
  • Smarter sparse execution detection for improved performance: GAMS can now automatically apply sparse execution to a broader set of simple parameter-constant comparisons, such as >, >=, <, or <= with positive or negative constants.
  • Improved error message in case of a redefinition error.
  • Using a Singleton Set as a domain for another symbol no longer raises an error.

GAMS Connect

GMSPython

  • Python has been upgraded to version 3.12.11.

Documentation

Installer

  • Windows installer:
    • Added support for self-hosted on-premises license servers.
    • Changed the installer to recognize 8-line licenses from the clipboard only.
    • No longer register .gpr file associations.
  • We plan to drop the simple self-extracting archives for macOS with the next major release.

Solvers

BARON

  • BARON is now also available for Linux on arm64.

CONOPT

  • New libraries 4.38.1.
    • Improved pre-processor to potentially select more post-triangular constraints.
    • Fixed potential infinite reinversion loop.
    • Fixed bug related to uninitialized values when computing the Hessian diagonal.

CPLEX

  • Fixed incorrect error message when using solution pool option .divflt.

GUROBI

  • The GAMS/GUROBI link has been rewritten and may behave differently in some cases. Please contact support@gams.com if there is any issue. As an immediate workaround, the old GAMS/GUROBI link is available as the hidden solver GUROBIOLD. It will be removed in a future release.
  • Removed support of deprecated dot option .genConstrType.

HiGHS

KNITRO

  • New libraries 15.0.1.
    • New Augmented Lagrangian (AL) algorithm for nonlinear optimization models. This new algorithm uses the nonlinearly constrained (i.e. NCL) approach and may still make use of second derivatives. It may be preferable for difficult problems with degenerate constraints where the Linear Independence Constraint Qualification (LICQ) is not satisfied. This algorithm can be selected by setting the user option nlp_algorithm = 6 (al).
    • New Primal-Dual Hybrid Gradient algorithm for linear programming (LP) problems. This new algorithm uses only first order information to converge and avoids matrix factorizations. It may be preferable for extremely large-scale models when the default interior-point method struggles. This algorithm can be selected by setting the new user option lp_algorithm = 4 (pdlp).
    • Significant performance improvements when using the limited-memory BFGS Hessian approximation (hessopt = 6), particularly on large-scale problems.
    • Updated Intel MKL and OpenMP to version 2024.2 on Windows and Linux x86_64 systems.
    • Performance improvements from presolve (bound propagation, reduced cost fixing, coefficient strengthening, parallel row detection), particularly for MINLPs with linear structures.
    • New option lp_algorithm: Indicates which algorithm to use to solve LPs.
    • New option nlp_algorithm: Indicates which algorithm to use to solve nonlinear problems (NLP and QCP).
    • New option mip_cutoff_abs: This value specifies the absolute improvement cutoff value for MIP.
    • New option mip_cutoff_rel: This value specifies the relative improvement cutoff value for MIP.
    • New option mip_node_lpalg: Specifies which algorithm to use for standard node LP subproblem solves in MIP (same values as lp_algorithm).
    • New option mip_node_nlpalg: Specifies which algorithm to use for standard node NLP subproblem solves in MIP (same values as nlp_algorithm).
    • New option mip_root_lpalg: Specifies which algorithm to use for root node LP subproblem solves in MIP (same values as lp_algorithm).
    • New option mip_root_nlpalg: Specifies which algorithm to use for root node NLP solves in MIP (same values as nlp_algorithm).
    • New option al_initpenalty: Specifies the initial penalty parameter value used in the Augmented Lagrangian (AL) algorithm.
    • New option al_maxpenalty: Specifies the maximum allowable penalty parameter value used in the Augmented Lagrangian (AL) algorithm.
    • New option value 9 of linsolver on macOS: Use parallel, non-deterministic Apple Sparse Solver.
    • New lower bound and default -1 of feastol, feastol_abs, opttol, and opttol_abs.
    • Fixed option bounds of delta, bar_conic_enable, bar_maxmu, bar_murule, mip_branchrule, and mip_terminate.
    • Changed options with type boolean to integer.
    • Deprecated option algorithm.
    • Removed options mip_lpalg, mip_nodealg, and mip_rootalg.

ReSHOP

  • New libraries 0.4.5.

XPRESS

  • The GAMS/XPRESS link has been rewritten and may behave differently in some cases. Please contact support@gams.com if there is any issue. As an immediate workaround, the old GAMS/XPRESS link is available as the hidden solver XPRESSOLD. It will be removed in a future release.
  • Removed option knitroOptFile: Use supported KNITRO options in the XPRESS options file instead. These new options are prefixed with knitro_, see also Knitro Options.
  • Changed behaviour of solnPoolMerge: Before, the model name got prefixed in addition to solnpoolPrefix. The new behaviour now matches the one of other solvers that support this feature.

Tools

FINDTHISGAMS

  • Dropped ide argument and no longer register .gpr file associations.

GAMS IDE

  • As announced the classic GAMS IDE was dropped from the system.

GAMS Studio

  • New version 1.22.1:
    • Added the gamsprobe output to the Copy System Information output of the GAMS Licensing dialog.
    • Added dynamic main file functionality. This will automatically set the current gms file as the project's main file when running the model.
    • Added additional system log messages in case a GAMS executable, like gams or gamsgetkey, is missing.
    • Added import functionality for project files from the classic GAMS IDE (*.gpr).
    • Added warnings for missing files when loading a Studio project.
    • Added On-Prem license server support.
    • Improved error messages for license installations via ALP.
    • Old style GAMS licenses are now ignored.
    • Improved Reference File Viewer with key navigation through symbols and references.
    • Improved the workflow of creating a new empty project.
    • Improved dynamic main file selection, i.e., instantly set the main file marker on tab change.
    • Fixed crash when reading a Studio project and the main gms file is missing.
    • Fixed tab menu to show only files of the focused project (when focused).
    • Fixed a crash when a project with an extension number, i.e., two projects having the same display name, is edited in the project options.
    • Fixed empty FileUsed Tab in Reference File Viewer when the file has been updated and reloaded.
    • Fixed a crash when opening a file containing an unknown schema data name in Connect Editor.
    • Fixed mouse scroll issue in log and lst-viewer on macOS, i.e., the scrolling is smooth now.
    • Fixed horizontal viewer tab scrolling, when one specific project is focused.
    • Fixed that directories in project options could not be changed when the default workdir wasn't defined (e.g., when starting with –ignore-settings).
    • Upgraded to Qt 6.9.2.

GDXDIFF, GDXDUMP, GDXMERGE

  • Fixed bug with handling of long absolute paths (>260 characters) on Windows and also make long relative paths work by automatically converting them into absolute paths internally.

MPS2GMS

  • Option CEQUATIONS is now deprecated and will be removed in a future version.

APIs

GAMS Transfer Python

  • Do not raise an error anymore when a Singleton Set is used as a domain for another symbol.

GDX

  • New libraries 7.11.17.
    • Include path to file that cannot be opened in error message of gdxOpenRead*.
    • Changed function signatures of gdxGetDLLVersion (to static method) and gdxErrorStr (to object method).

GEV

  • Add function gevGetLSCBInfo to extract and return the log/status write callback and its associated callback data pointer from the lshandle returned by gevSwitchLogStat.

GMO

  • Added function gmoUpdateJac: This function updates the value of linear Jacobian entries created by gmoAddRow or gmoAddCol.

Python

  • As announced, support for numpy 1, and pandas before 2.2.2 has been dropped.
  • Added preliminary support for Python 3.14. As Python 3.14 has not yet been officially released, full compatibility cannot be guaranteed.

Solver links

  • Library initialization and finalization functions (xyzInitialize and xyzFinalize) of solver link libraries are deprecated, because they were not called as expected if the same solver link library was used by several CFG objects simultaneously. Instead, it is advised to use proper library initialization/finalization mechanism, e.g., __attribute(constructor/destructor)__ and DllMain. CFG currently prints a warning if these methods are found, but will still call them. In a future GAMS version, this warning will be changed to an error.

Model Libraries

GAMS Model Library

GAMS Test Library

51.2.0 Minor release (September 29, 2025)

Acknowledgments

We would like to thank all of our users who have reported problems and made suggestions for improving this release. In particular, we thank Juan Pablo Vasco Cano, Bruce McCarl, and Feng-Sheng Wang.

GAMS System

GAMS

  • GAMS no longer issues a compilation error when Action=CompileOnly (a=c) is used and the solver specified on the command line is not installed. This change allows models to be compiled on one system and for execution on another, which is particularly useful for remote services like GAMS Engine or NEOS.
  • Fixed failing license check in the next-generation GAMS compiler (accessible via option CompilerPreview (cp)).

GAMS Connect

  • Fixed a bug where the ExcelReader agent failed to create empty symbols.

Solvers

BARON

  • New libraries 25.9.13.

ReSHOP

  • New libraries 0.4.6.

Tools

GAMS Studio

  • New version 1.22.2:
    • Improved license validation log, i.e., all messages of the license validation are written to the system log now.
    • Improved behavior of Solver Option Editor and Parameter File Editor:
      • Double clicking an enumerated value of an option adds the description of the enumerated value instead of the option to the comment column.
      • Enabling the Open As Text button always and checking, when clicked, whether a file has been modified before.
      • Removing unnecessary error messages when pressing + icon to add/append new option.
    • Fixed incorrect behavior of Solver Option Editor:
      • Editing an empty string value for a string option with a defined default value no longer replaced by the comment.
      • Dragging and dropping an option no longer adds multiple rows of the option.
      • Replacing an existing option row by drag and drop no longer crashes Studio.
    • Fixed incorrect ESC key behavior in Parameter File Editor, Solver Option Editor, and GAMS User Configuration Editor.
    • Fixed that the S&R dialog wildcard include and exclude file filters did not match all expected files.
    • Fixed that changes to command line parameters were lost when changing the main file.
    • Fixed that Studio couldn't start more than 11 GAMS jobs in parallel.
    • Fixed update modification state when the 'Dynamic main file' setting has changed.

Model Libraries

GAMS Test Library