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<html>
<head>
<title>
CNF_IO - Read or Write a CNF File
</title>
</head>
<body bgcolor="#EEEEEE" link="#CC0000" alink="#FF3300" vlink="#000055">
<h1 align = "center">
CNF_IO <br> Read or Write a CNF File
</h1>
<hr>
<p>
<b>CNF_IO</b>
is a C++ library which
can read or write a file, in the DIMACS CNF format, containing
information about a boolean formula written in conjunctive normal form.
</p>
<p>
Boolean expressions, written in conjunctive normal form, may be used
as test cases for the satisfiability problem. That problem seeks to
determine all possible combinations of variable values that result in
the formula being evaluated as TRUE.
</p>
<p>
The routines in <b>CNF_IO</b> are intended to make it possible to
transfer information between a CNF file and a computer program.
</p>
<h3 align = "center">
Licensing:
</h3>
<p>
The computer code and data files described and made available on this web page
are distributed under
<a href = "../../txt/gnu_lgpl.txt">the GNU LGPL license.</a>
</p>
<h3 align = "center">
Languages:
</h3>
<p>
<b>CNF_IO</b> is available in
<a href = "../../cpp_src/cnf_io/cnf_io.html">a C++ version</a> and
<a href = "../../f77_src/cnf_io/cnf_io.html">a FORTRAN77 version</a> and
<a href = "../../f_src/cnf_io/cnf_io.html">a FORTRAN90 version.</a>
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../data/cnf/cnf.html">
CNF</a>,
a data directory which
describes the DIMACS CNF file format for specifying instances of the
satisfiability problem for boolean formulas in conjunctive normal form.
</p>
<p>
<a href = "../../cpp_src/satisfy/satisfy.html">
SATISFY</a>,
a C++ program which
demonstrates, for a particular circuit, an exhaustive search
for solutions of the circuit satisfiability problem.
</p>
<h3 align = "center">
Reference:
</h3>
<p>
<ol>
<li>
Rina Dechter,<br>
Enhancement Schemes for constraint processing:
Backjumping, learning, and cutset decomposition,<br>
Artificial Intelligence,<br>
Volume 41, Number 3, January 1990, pages 273-312.
</li>
</ol>
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "cnf_io.cpp">cnf_io.cpp</a>, the source code.
</li>
<li>
<a href = "cnf_io.hpp">cnf_io.hpp</a>, the include file.
</li>
<li>
<a href = "cnf_io.sh">cnf_io.sh</a>,
commands to compile the source code.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "cnf_io_prb.cpp">cnf_io_prb.cpp</a>,
a sample calling program.
</li>
<li>
<a href = "cnf_io_prb.sh">cnf_io_prb.sh</a>,
commands to compile and run the sample program.
</li>
<li>
<a href = "cnf_io_prb_output.txt">cnf_io_prb_output.txt</a>,
the output file.
</li>
<li>
<a href = "test01_v3_c2.cnf">test01_v3_c2.cnf</a>,
a CNF file, for 3 variables and 2 clauses, written by the sample program.
</li>
<li>
<a href = "test02_v6_c18.cnf">test02_v16_c18.cnf</a>,
a CNF file, for 16 variables and 18 clauses, written by the sample program.
</li>
</ul>
</p>
<h3 align = "center">
List of Routines:
</h3>
<p>
<ul>
<li>
<b>CH_CAP</b> capitalizes a single character.
</li>
<li>
<b>CH_EQI</b> is true if two characters are equal, disregarding case.
</li>
<li>
<b>CH_IS_SPACE</b> is TRUE if a character represents "white space".
</li>
<li>
<b>CNF_DATA_READ</b> reads the data of a CNF file.
</li>
<li>
<b>CNF_DATA_WRITE</b> writes data to a CNF file.
</li>
<li>
<b>CNF_EVALUATE</b> evaluates a formula in CNF form.
</li>
<li>
<b>CNF_HEADER_READ</b> reads the header of a CNF file.
</li>
<li>
<b>CNF_HEADER_WRITE</b> writes the header for a CNF file.
</li>
<li>
<b>CNF_PRINT</b> prints CNF information.
</li>
<li>
<b>CNF_WRITE</b> writes the header and data of a CNF file.
</li>
<li>
<b>I4_POWER</b> returns the value of I^J.
</li>
<li>
<b>LVEC_NEXT</b> generates the next logical vector.
</li>
<li>
<b>S_ADJUSTL</b> flushes a string left.
</li>
<li>
<b>S_BLANKS_DELETE</b> replaces consecutive blanks by one blank.
</li>
<li>
<b>S_EQI</b> reports whether two strings are equal, ignoring case.
</li>
<li>
<b>S_LEN_TRIM</b> returns the length of a string to the last nonblank.
</li>
<li>
<b>S_TO_I4</b> reads an I4 from a string.
</li>
<li>
<b>S_WORD_EXTRACT_FIRST</b> extracts the first word from a string.
</li>
<li>
<b>TIMESTAMP</b> prints the current YMDHMS date as a time stamp.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../cpp_src.html">
the C++ source codes</a>.
</p>
<hr>
<i>
Last revised on 09 June 2008.
</i>
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