Introduction

The CUDD package provides functions to manipulate Binary Decision Diagrams (BDDs) [5,3], Algebraic Decision Diagrams (ADDs) [1], and Zero-suppressed Binary Decision Diagrams (ZDDs) [12]. BDDs are used to represent switching functions; ADDs are used to represent function from $\{0,1\}^n$ to an arbitrary set. ZDDs represent switching functions like BDDs; however, they are much more efficient than BDDs when the functions to be represented are characteristic functions of cube sets, or in general, when the ON-set of the function to be represented is very sparse. They are inferior to BDDs in other cases.

The package provides a large set of operations on BDDs, ADDs, and ZDDs, functions to convert BDDs into ADDs or ZDDs and vice versa, and a large assortment of variable reordering methods.

The CUDD package can be used in three ways:

• As a black box. In this case, the application program that needs to manipulate decision diagrams only uses the exported functions of the package. The rich set of functions included in the CUDD package allows many applications to be written in this way. Section 3 describes how to use the exported functions of the package. An application written in terms of the exported functions of the package needs not concern itself with the details of variable reordering, which may take place behind the scenes. Click here for a list of the exported functions.
• As a clear box. When writing a sophisticated application based on decision diagrams, efficiency often dictates that some functions be implemented as direct recursive manipulation of the diagrams, instead of being written in terms of existing primitive functions. Section 4 explains how to add new functions to the CUDD package. It also details how to write a recursive function that can be interrupted by dynamic variable reordering. Click here for a list of the exported and internal functions.
• Through an interface. Object-oriented languages like C++ and Perl5 can free the programmer from the burden of memory management. A C++ interface is included in the distribution of CUDD. It automatically frees decision diagrams that are no longer used by the application and overloads operators. Almost all the functionality provided by the CUDD exported functions is available through the C++ interface, which is especially recommended for fast prototyping. Section 5 explains how to use the interface. A Perl5 interface also exists and is ditributed separately. (See Section 2.2.) Some applications define their own interfaces. See for example Section 3.17.

In the following, the reader is supposed to be familiar with the basic ideas about decision diagrams, as found, for instance, in [3].