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<html>
<head>
<title>
MACHAR - Dynamic Computation of Machine Constants
</title>
</head>
<body bgcolor="#EEEEEE" link="#CC0000" alink="#FF3300" vlink="#000055">
<h1 align = "center">
MACHAR <br> Dynamic Computation of Machine Constants
</h1>
<hr>
<p>
<b>MACHAR</b>
is a MATLAB library which
dynamically computes constants that
characterize the floating point arithmetic system on a computer,
by William Cody.
</p>
<p>
The constants include
the value of the "machine epsilon", the smallest number that can
be added to 1 and make a difference. However, it includes many
other quantities of interest, including the arithmetic base,
the largest and smallest magnitudes, and so on.
</p>
<p>
The default variable type in MATLAB is similar to a double precision
complex variable. When doing real arithmetic, this means that
calculations are done in double precision. MATLAB also offers
a function called <b>single</b> that can be used to convert a
value to a single precision real value. When used to initialize
a variable, <b>single</b> effectively "declares" that variable to
be a single precision real variable.
</p>
<p>
The FORTRAN77 version of these routines was supplied as part of ACM
TOMS algorithm 665.
</p>
<p>
A C version of these routines was supplied as part of ACM
TOMS algorithm 722.
</p>
<p>
Note that "Numerical Recipes" includes a listing and discussion
of MACHAR.
</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>MACHAR</b> is available in
<a href = "../../c_src/machar/machar.html">a C version</a> and
<a href = "../../cpp_src/machar/machar.html">a C++ version</a> and
<a href = "../../f77_src/machar/machar.html">a FORTRAN77 version</a> and
<a href = "../../f_src/machar/machar.html">a FORTRAN90 version</a> and
<a href = "../../m_src/machar/machar.html">a MATLAB version</a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../m_src/machine/machine.html">
MACHINE</a>,
a MATLAB library which
stores the appropriate values of machine constants for a given machine.
</p>
<h3 align = "center">
Author:
</h3>
<p>
Original FORTRAN77 version by William Cody.
MATLAB version by John Burkardt.
</p>
<h3 align = "center">
Reference:
</h3>
<p>
<ol>
<li>
William Cody,<br>
Algorithm 665:
MACHAR, a subroutine to dynamically determine
machine parameters,<br>
ACM Transactions on Mathematical Software,<br>
Volume 14, Number 4, December 1988, pages 303-311.
</li>
<li>
William Cody, William Waite,<br>
Software Manual for the Elementary Functions,<br>
Prentice Hall, 1980,<br>
ISBN: 0138220646,<br>
LC: QA331.C635.
</li>
<li>
Morven Gentleman, Scott Marovich,<br>
More on Algorithms that Reveal Properties of Floating Point
Arithmetic Units,<br>
Communications of the ACM,<br>
Volume 17, Number 5, May 1974, pages 276-277.
</li>
<li>
Michael Malcolm,<br>
Algorithms to Reveal Properties of Floating Point Arithmetic,<br>
Communications of the ACM,<br>
Volume 15, Number 11, November 1972, pages 949-951.
</li>
<li>
William Press, Brian Flannery, Saul Teukolsky, William Vetterling,<br>
Numerical Recipes in FORTRAN: The Art of Scientific Computing,<br>
Second Edition,<br>
Cambridge University Press, 1992,<br>
ISBN: 0-521-43064-X,<br>
LC: QA297.N866.
</li>
</ol>
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "r4_machar.m">r4_machar.m</a>,
determines single precision machine constants.
</li>
<li>
<a href = "r8_machar.m">r8_machar.m</a>,
determines double precision machine constants.
</li>
<li>
<a href = "timestamp.m">timestamp.m</a>,
prints the current YMDHMS date as a time stamp.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "machar_test.m">machar_test.m</a>,
calls all the tests.
</li>
<li>
<a href = "machar_test01.m">machar_test01.m</a>,
tests R4_MACHAR.
</li>
<li>
<a href = "machar_test02.m">machar_test02.m</a>,
tests R8_MACHAR.
</li>
<li>
<a href = "machar_test_output.txt">machar_test_output.txt</a>,
the output file.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../m_src.html">
the MATLAB source codes</a>.
</p>
<hr>
<i>
Last revised on 02 June 2012.
</i>
<!-- John Burkardt -->
</body>
</html>