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<html>
<head>
<title>
SORT_RC - Sort Using Reverse Communication
</title>
</head>
<body bgcolor="#eeeeee" link="#cc0000" alink="#ff3300" vlink="#000055">
<h1 align = "center">
SORT_RC <br> Sort Using Reverse Communication
</h1>
<hr>
<p>
<b>SORT_RC</b>
is a C++ library which
can sort a list of any kind of objects,
using reverse communication (RC).
</p>
<p>
The program works by repeatedly asking the user to compare two
items on the list. The user is free to carry out the comparison
in the calling program, in any desired way.
</p>
<p>
A typical usage, to sort an array of 100 items, might look
something like this:
<pre>
n = 100
indx = 0 -- Indicates the beginning of a sort
begin loop
sort_rc ( n, &indx, &i, &j, isgn )
if ( indx < 0 ) (Compare items I and J)
if ( a[i-1] <= a[j-1] )
isgn = -1
else
isgn = +1
else if ( 0 < indx ) (Swap items I and J)
k = a[i-1]
a[i-1] = a[j-1]
a[j-1] = k
else
break from loop
end loop
</pre>
</p>
<p>
The original version of sort_rc() requires the use of several variables
declared internally to the function, whose values must be preserved
between calls. The conventions for such computations vary from language
to language; moreover, this kind of approach means that a single copy of
the function cannot handle multiple requests for computation that might
arise, especially in parallel computations. For that reason, a revised
function, called sort_safe_rc(), is available, which does not rely on
hidden internal variables and may safely be used to manage multiple
simultaneous sorts.
</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>SORT_RC</b> is available in
<a href = "../../c_src/sort_rc/sort_rc.html">a C version</a> and
<a href = "../../cpp_src/sort_rc/sort_rc.html">a C++ version</a> and
<a href = "../../f77_src/sort_rc/sort_rc.html">a FORTRAN77 version</a> and
<a href = "../../f_src/sort_rc/sort_rc.html">a FORTRAN90 version</a> and
<a href = "../../m_src/sort_rc/sort_rc.html">a MATLAB version</a> and
<a href = "../../py_src/sort_rc/sort_rc.html">a Python version</a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../cpp_src/backtrack_binary_rc/backtrack_binary_rc.html">
BACKTRACK_BINARY_RC</a>,
a C++ library which
carries out a backtrack search for a set of binary decisions, using
reverse communication.
</p>
<p>
<a href = "../../cpp_src/bisection_rc/bisection_rc.html">
BISECTION_RC</a>,
a C++ library which
seeks a solution to the equation F(X)=0 using bisection
within a user-supplied change of sign interval [A,B].
The procedure is written using reverse communication.
</p>
<p>
<a href = "../../cpp_src/cg_rc/cg_rc.html">
CG_RC</a>,
a C++ library which
implements the conjugate gradient (CG) method for solving
a positive definite sparse linear system A*x=b,
using reverse communication (RC).
</p>
<p>
<a href = "../../cpp_src/subset/subset.html">
SUBSET</a>,
a C++ library which
enumerates, generates, randomizes, ranks and unranks combinatorial objects
including combinations, compositions, Gray codes, index sets, partitions,
permutations, polynomials, subsets, and Young tables. Backtracking
routines are included to solve some combinatorial problems.
</p>
<p>
<a href = "../../cpp_src/zero_rc/zero_rc.html">
ZERO_RC</a>,
a C++ library which
seeks solutions of a scalar nonlinear equation f(x) = 0,
or a system of nonlinear equations,
using reverse communication.
</p>
<h3 align = "center">
Reference:
</h3>
<p>
<ol>
<li>
Albert Nijenhuis, Herbert Wilf,<br>
Combinatorial Algorithms for Computers and Calculators,<br>
Second Edition,<br>
Academic Press, 1978,<br>
ISBN: 0-12-519260-6,<br>
LC: QA164.N54.
</li>
</ol>
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "sort_rc.cpp">sort_rc.cpp</a>, the source code;
</li>
<li>
<a href = "sort_rc.hpp">sort_rc.hpp</a>, the include file;
</li>
<li>
<a href = "sort_rc.sh">sort_rc.sh</a>,
commands to compile the source code;
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "sort_rc_prb.cpp">sort_rc_prb.cpp</a>, the calling program;
</li>
<li>
<a href = "sort_rc_prb.sh">sort_rc_prb.sh</a>, commands to compile,
link and run the calling program;
</li>
<li>
<a href = "sort_rc_prb_output.txt">sort_rc_prb_output.txt</a>,
the output file.
</li>
</ul>
</p>
<h3 align = "center">
List of Routines:
</h3>
<p>
<ul>
<li>
<b>I4VEC_PRINT</b> prints an I4VEC.
</li>
<li>
<b>I4VEC_UNIFORM_AB</b> returns a scaled pseudorandom I4VEC.
</li>
<li>
<b>SORT_RC</b> externally sorts a list of items into ascending order.
</li>
<li>
<b>SORT_SAFE_RC</b> externally sorts a list of items into ascending order.
</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 10 March 2015.
</i>
<!-- John Burkardt -->
</body>
</html>