First Project: Satisfiability Solvers

Due Date: Friday, May 5, 2000

In this project you will implement a systematic satisfiability solver and a stochastic one, and study them experimentally.

What to do:

What to turn in:

We may ask you to do a demo / oral discussion of the project.
Acceptable languages for the project are: LISP, C/C++, and Java. Other languages may be allowed by special request.

Background reading:

(Not indispensable, but helpful.) Much of the recent research on satisfiability has appeared in AAAI, the National Conference on Artificial Intelligence. The proceedings are available in the library, and many of the papers can be found online.

Standard file formats to be used:

Your sat-solver should accept files of the following format:
Where numvars, numclauses and clauselength are integers and the format for a clause is a parenthesized list of literals.
( lit1 lit2 ... litm )
Literals will be represented by integers, with negated literals represented by negative numbers. For example, the 5-clause, 4-variable 3-CNF formula
( A1 v ~A2 v A3) ^ ( ~A3 v ~A1 v A4 ) ^ ( A2 v A1 v ~A4 ) 
  ^ ( ~A2 v A3 v ~A4) v ( ~A1 v A2 v A3 )
Would be represented by the file:
( 1 -2 3 )
( -3 -1 4 )
( 2 1 -4 )
( -2 3 -4 )
( -1 2 3 )
The program should have, somewhere in its output, a line that reads "Solution:" followed by a line with the string "Fail" if no solution was found or a parenthesized list of variable assignments sorted by variable number.  So for the input above, the program might print:
( 1 2 -3 -4 )
Meaning that the variable assignment:
A1 = True, A2 = True, A3 = False, A4 = False
was found as a solution to this problem.

Note the spaces before and after each literal in the above i/o formats. The grading program will require that you follow the correct format exactly.

Your program should be able to read the test file from the standard input stream. Any parameters your program uses should be set using command line options.  For example, if you want to be able to control the number of restarts and flips, you should create command line options.

walksat -r10000 -f1000 < problem.wff > problem.out
The generate program should take at least three inputs: numvars, numclauses and clauselen. Any other inputs you'd like to specify should be clearly documented.

Code provided:

To help with the experimentation phase, we are providing some infrastructure. The file will do multiple runs of your program over test files.  See the file itself for a description of how to use it.  The file will check that the solution returned by your solver is valid.  They're both perl scripts, so after saving them on a unix system, you'll have to make them executable. (The previous version of is renamed to and is here.)
chmod 700
Finally you can download to generate valid problems.

Good luck!