### 34.1 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:

- Two classes of constraints are handled internally: primitive constraints
and global constraints.
- The constraints described in this chapter are automatically translated
to conjunctions of primitive and global library constraints.
- The truth value of a primitive constraint can be reflected into a 0/1-variable
(reification).
- New primitive constraints can be added by writing so-called indexicals.
- New global constraints can be written in Prolog, by means of a
programming interface.

This library fully supports multiple SICStus run-times 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 example programs are given in
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. The solver's execution mechanism and primitives are
described in The Constraint System. 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.