techniques.PL
Class CNF

java.lang.Object
  |
  +--techniques.PL.CNF

public final class CNF

extends java.lang.Object

A set of utilities for dealing with propositional logic sentences in conjunctive normal form (CNF).

Constructor Summary

CNF()

 

Method Summary
static boolean	coinFlip()           Returns true with probability 0.5.
static void	main(java.lang.String[] args)           A command-line accessible version of the randInstance() method.
static Conjunction	parse(java.io.File infile)           Parses a textfile into a Conjunction.
static Conjunction	parse(java.lang.String sentence)           Parses a String into a Conjunction.
static java.lang.String	randDisjunction()           Returns a disjunction of three literals chosen by randLiteral()
static java.lang.String	randInstance(int numClauses)           Returns a randomly generated 3-SAT instance, as a String.
static int	randInt(int a, int b)           returns a random integer between a and b, inclusive.
static java.lang.String	randLiteral()           Returns a random literal, as a string.

 

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Constructor Detail

CNF

public CNF()

parse

public static Conjunction parse(java.lang.String sentence)

Parses a String into a Conjunction. This Parser does very little error checking. Unparsable sentences will either produce garbage or a runtime Exception. Whitespace is insignificant.

parse

public static Conjunction parse(java.io.File infile)

Parses a textfile into a Conjunction. If there is an IO Error, this method will print an error message and returns null. Otherwise, this Parser does very little error checking. Unparsable sentences will either produce garbage or a runtime Exception. Whitespace in the file is insignificant.

main

public static void main(java.lang.String[] args)

A command-line accessible version of the randInstance() method. It takes one mandatory and one optional argument. The first argument is a real number indicating the ratio of clauses to variables in the returned instance. The second (optional) argument is a filename in which to write the results. If no second argument is supplied, the sentence will be sent to standard out.

For example:

% java techniques.PL.CNF 2.2 mysentence.cnf

will result in a sentence with 57 clauses (about 2.2*26), written to a file named mysentence.cnf. See randInstance() for more documentation.

randInstance

public static java.lang.String randInstance(int numClauses)

Returns a randomly generated 3-SAT instance, as a String. All sentences are drawn from a world of 26 variables, A-Z. numClauses is the number of disjunctive clauses to generate.

randDisjunction

public static java.lang.String randDisjunction()

Returns a disjunction of three literals chosen by randLiteral()

randLiteral

public static java.lang.String randLiteral()

Returns a random literal, as a string. The variable of the literal is drawn uniformly from 'A'-'Z', and negated with probability 0.5.

coinFlip

public static boolean coinFlip()

Returns true with probability 0.5.

randInt

public static int randInt(int a,
                          int b)

returns a random integer between a and b, inclusive.