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wtime.html
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wtime.html
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<html>
<head>
<title>
WTIME - Compute Elapsed Wallclock Time
</title>
</head>
<body bgcolor="#EEEEEE" link="#CC0000" alink="#FF3300" vlink="#000055">
<h1 align = "center">
WTIME <br> Compute Elapsed Wallclock Time
</h1>
<hr>
<p>
<b>WTIME</b>
is a FORTRAN90 library which
returns a reading of the wall clock time.
</p>
<p>
For parallel programming, the important thing to measure is the elapsed
wallclock time. This can be found by subtracting an initial reading of
the wallclock time from a final one.
</p>
<p>
The OpenMP system provides a function used as follows:
<pre>
seconds = omp_get_wtime ( )
operations to time;
seconds = omp_get_wtime ( ) - seconds;
</pre>
while the MPI system provides a similar function used as:
<pre>
seconds = MPI_Wtime ( );
operations;
seconds = MPI_Wtime ( ) - seconds;
</pre>
and in MATLAB, wallclock time can be taken with "tic" and "toc":
<pre>
tic;
operation;
seconds = toc;
</pre>
</p>
<p>
WTIME provides a way to get a similar reading:
<pre>
seconds = wtime ( );
operations;
seconds = wtime ( ) - seconds;
</pre>
</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>WTIME</b> is available in
<a href = "../../c_src/wtime/wtime.html">a C version</a> and
<a href = "../../cpp_src/wtime/wtime.html">a C++ version</a> and
<a href = "../../f77_src/wtime/wtime.html">a FORTRAN77 version</a> and
<a href = "../../f_src/wtime/wtime.html">a FORTRAN90 version</a> and
<a href = "../../m_src/wtime/wtime.html">a MATLAB version</a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../f_src/timer/timer.html">
TIMER</a>,
a FORTRAN90 program which
shows how to compute the elapsed CPU time inside a program.
</p>
<p>
<a href = "../../f_src/timestamp/timestamp.html">
TIMESTAMP</a>,
a FORTRAN90 library which
displays the current wall clock time.
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "wtime.f90">wtime.f90</a>,
the source code.
</li>
<li>
<a href = "wtime.sh">wtime.sh</a>,
commands to compile the source code.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "wtime_prb.f90">wtime_prb.f90</a>,
a sample calling program.
</li>
<li>
<a href = "wtime_prb.sh">wtime_prb.sh</a>,
commands to compile, link and run the sample calling program.
</li>
<li>
<a href = "wtime_prb_output.txt">wtime_prb_output.txt</a>,
the output file.
</li>
</ul>
</p>
<h3 align = "center">
List of Routines:
</h3>
<p>
<ul>
<li>
<b>WTIME</b> returns a reading of the wall clock time.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../f_src.html">
the FORTRAN90 source codes</a>.
</p>
<hr>
<i>
Last revised on 27 April 2009.
</i>
<!-- John Burkardt -->
</body>
</html>