PyCSP3-Scheduling: A Scheduling Extension for PyCSP3

TL;DR

PyCSP3 Scheduling extends the PyCSP3 framework with native scheduling abstractions, enabling more natural modeling of scheduling problems and efficient compilation to standard constraints.

Contribution

It introduces a library adding scheduling abstractions to PyCSP3, with dedicated constraints and expressions, preserving the modeling/solving separation and supporting compilation to XCSP3.

Findings

Identical objectives on all optimal pairs across 17 model families.

Nearly half of the model families remain structurally unchanged after compilation.

Performance varies, with some instances up to 5.8x faster and others slower due to compilation overhead.

Abstract

PyCSP$^3$ provides a productive way to build constraint models for solving combinatorial constrained problems and export them to XCSP$^3$, preserving a complete separation between modeling and solving. However, it lacks native support for scheduling abstractions such as interval variables, sequence variables, and resource functions. As a result, scheduling models must be encoded with low-level integer variables and manual channeling constraints, even though PyCSP$^3$ already provides global constraints like NoOverlap and Cumulative on integer arrays. We present PyCSP$^3$ Scheduling, a library that adds scheduling abstractions to PyCSP$^3$ through 53 dedicated constraints and 27 expressions, and compiles them down to standard PyCSP$^3$/XCSP$^3$ constraints, maintaining the modeling/solving separation that underpins the PyCSP$^3$ ecosystem. On 261 paired instances across 17 model families (5 runs each), both formulations produce identical objectives on all 72 doubly-proved optimal pairs and nearly half of the families (8/17) remain structurally unchanged after compilation; however, runtime performance diverges across families, with clear gains on some (up to 5.8x) and regressions on others due to the overhead of compilation decompositions. Code and benchmarks are available at: https://github.com/sohaibafifi/pycsp3-scheduling