Comentários sobre o pacote GAMS

       The General Algebraic Modeling System (GAMS) is specifically designed for modeling linear, nonlinear and mixed integer optimization problems. The system is especially useful with large, complex problems. GAMS is available for use on personal computers, workstations, mainframes and supercomputers.

       GAMS allows the user to concentrate on the modeling problem by making the setup simple. The system takes care of the time-consuming details of the specific machine and system software implementation.

       GAMS is especially useful for handling large, complex, one-of-a-kind problems which may require many revisions to establish an accurate model. The system models problems in a highly compact and natural way. The user can change the formulation quickly and easily, can change from one solver to another, and can even convert from linear to nonlinear with little trouble.

       System Features

       GAMS lets the user concentrate on modeling. By eliminating the need to think about purely technical machine-specific problems such as address calculations, storage assignments, subroutine linkage, and input-output and flow control, GAMS increases the time available for conceptualizing and running the model, and analyzing the results. GAMS structures good modeling habits itself by requiring concise and exact specification of entities and relationships. The GAMS language is formally similar to commonly used programming languages. It is therefore familiar to anyone with programming experience.

       Using GAMS, data are entered only once in familiar list and table form. Models are described in concise algebraic statements which are easy for both humans and machines to read. Whole sets of closely related constraints are entered in one statement. GAMS automatically generates each constraint equation, and lets the user make exceptions in cases where generality is not desired. Statements in models can be reused without having to change the algebra when other instances of the same or related problems arise. The location and type of errors are pinpointed before a solution is attempted. GAMS handles dynamic models involving time sequences, lags and leads and treatment of temporal endpoints.

       GAMS is flexible and powerful. Models are fully portable from one computer platform to another when GAMS is loaded to each platform. GAMS facilitates sensitivity analysis. The user can easily program a model to solve for different values of an element and then generate an output report listing the solution characteristics for each case. Models can be developed and documented simultaneously because GAMS allows the user to include explanatory text as part of the definition of any symbol or equation.

Comentários sobre o pacote XPRESS

       Xpress-Mosel is a modeling and solving environment and language, supported by Xpress-Optimizer. It can be run from (a) the command prompt (console), (b) the Windows development environment Xpress-IVE, or (c) from a C or other programming interface.

       Xpress-SP is a Stochastic Programming tool for solving optimization problems involving uncertainty. Xpress-SP can be used to model and solve problems occurring in Supply Chain Management, Energy, Finance, Transportation, etc., by building uncertainty into the optimization problem in order to hedge against future variability. By assimilating uncertainty into the optimization process, Xpress-SP enables superior management of resources by eliminating the overhead costs of conservative planning, reducing penalties for unmet targets, and achieving higher service levels and profits.

       Traditionally, Stochastic Programming has been a difficult to approach area due to the complexity of modeling uncertainty, particularly for multi-stage problems. Xpress-SP has simplified the process of modeling stochastic problems by seamlessly integrating SP modeling facilities within Xpress-Mosel and Xpress-IVE.