10.9.1 Introduction

The clp(FD) solver described in this chapter is an instance of the general Constraint Logic Programming scheme introduced in [Jaffar & Michaylov 87]. This constraint domain is particularly useful for modeling discrete optimization and verification problems such as scheduling, planning, packing, timetabling etc. The treatise [Van Hentenryck 89] is an excellent exposition of the theoretical and practical framework behind constraint solving in finite domains, and summarizes the work up to 1989.

This solver has the following highlights:

• A rich set of global constraints with state-of-the-art propagators.
• Two classes of propagators are handled internally: indexicals and global propagators.
• Propagators of both classes can be user-defined, by means of programming interfaces.
• The constraints described in this chapter are automatically translated to sets of propagators.
• The truth value of a primitive constraint can be reflected into a 0/1-variable, i.e. a variable with domain 0..1 (reification).

This library fully supports multiple SICStus runtimes in a process.

The rest of this chapter is organized as follows: How to load the solver and how to write simple programs is explained in CLPFD Interface. A description of all constraints that the solver provides is contained in Available Constraints. The predicates for searching for solution are documented in Enumeration Predicates. The predicates for getting execution statistics are documented in Statistics Predicates. A few notes on debugging are given in CLPFD Debugging. A few example programs are given in CLPFD Example Programs. Finally, Syntax Summary contains syntax rules for all expressions.

The following sections discuss advanced features and are probably only relevant to experienced users: How to control the amount of information presented in answers to queries is explained in Answer Constraints. How to add new global constraints via a programming interface is described in Defining Global Constraints. How to define new primitive constraints with indexicals is described in Defining Primitive Constraints. The fine points of coexisting with attributes and blocked goals are described in CLPFD Coexisting.