Gecode

Gecode, short for Generic Constraint Development Environment, is an open-source toolkit for constraint programming. It provides a reusable, high-performance C++ library for modeling and solving constraint satisfaction problems and constraint optimization problems.

The library centers on declaring variables, posting constraints, and configuring a search strategy. It offers finite-domain variables (such as IntVar and BoolVar), along with other types like SetVar, and provides a broad set of propagators for effective domain filtering. Gecode includes numerous global constraints and supports reified constraints, enabling the logical linking of constraints to boolean variables.

Propagation and search are core to Gecode. The modular propagation engine prunes variable domains as constraints are posted, and users can tailor search with various branching strategies and search engines, including both sequential and parallel exploration of the search space.

Architecture and usage: A model is built by deriving a Space and implementing a build method in which variables are created and constraints posted. Solving is performed by a search procedure that traverses the space to enumerate solutions or optimize an objective. Gecode can be used directly through its C++ API or as a backend solver for modeling languages such as MiniZinc.

License and availability: The project is open-source under a permissive BSD-like license and is portable across major platforms, including Linux, Windows, and macOS. Its design emphasizes performance, modularity, and extensibility, making it suitable for both research and practical applications.

Applications: Gecode is employed in academic research and industry to address problems in scheduling, rostering, resource allocation, and planning, where constraint-based reasoning provides robust and flexible modeling capabilities.