Mercurial > hg > batch-feature-extraction-tool
diff Lib/fftw-3.2.1/doc/html/Simple-MPI-example.html @ 15:585caf503ef5 tip
Tidy up for ROLI
| author | Geogaddi\David <d.m.ronan@qmul.ac.uk> |
|---|---|
| date | Tue, 17 May 2016 18:50:19 +0100 |
| parents | 636c989477e7 |
| children |
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--- a/Lib/fftw-3.2.1/doc/html/Simple-MPI-example.html Wed May 04 11:02:59 2016 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,149 +0,0 @@ -<html lang="en"> -<head> -<title>Simple MPI example - FFTW 3.2alpha3</title> -<meta http-equiv="Content-Type" content="text/html"> -<meta name="description" content="FFTW 3.2alpha3"> -<meta name="generator" content="makeinfo 4.8"> -<link title="Top" rel="start" href="index.html#Top"> -<link rel="up" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" title="Distributed-memory FFTW with MPI"> -<link rel="prev" href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" title="Linking and Initializing MPI FFTW"> -<link rel="next" href="MPI-data-distribution.html#MPI-data-distribution" title="MPI data distribution"> -<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> -<!-- -This manual is for FFTW -(version 3.2alpha3, 14 August 2007). - -Copyright (C) 2003 Matteo Frigo. - -Copyright (C) 2003 Massachusetts Institute of Technology. - - Permission is granted to make and distribute verbatim copies of - this manual provided the copyright notice and this permission - notice are preserved on all copies. - - Permission is granted to copy and distribute modified versions of - this manual under the conditions for verbatim copying, provided - that the entire resulting derived work is distributed under the - terms of a permission notice identical to this one. - - Permission is granted to copy and distribute translations of this - manual into another language, under the above conditions for - modified versions, except that this permission notice may be - stated in a translation approved by the Free Software Foundation. - --> -<meta http-equiv="Content-Style-Type" content="text/css"> -<style type="text/css"><!-- - pre.display { font-family:inherit } - pre.format { font-family:inherit } - pre.smalldisplay { font-family:inherit; font-size:smaller } - pre.smallformat { font-family:inherit; font-size:smaller } - pre.smallexample { font-size:smaller } - pre.smalllisp { font-size:smaller } - span.sc { font-variant:small-caps } - span.roman { font-family:serif; font-weight:normal; } - span.sansserif { font-family:sans-serif; font-weight:normal; } ---></style> -</head> -<body> -<div class="node"> -<p> -<a name="Simple-MPI-example"></a> -Next: <a rel="next" accesskey="n" href="MPI-data-distribution.html#MPI-data-distribution">MPI data distribution</a>, -Previous: <a rel="previous" accesskey="p" href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW">Linking and Initializing MPI FFTW</a>, -Up: <a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a> -<hr> -</div> - -<h3 class="section">6.3 Simple MPI example</h3> - -<p>Before we document the FFTW MPI interface in detail, we begin with a -simple example outlining how one would perform a two-dimensional -<code>N0</code> by <code>N1</code> complex DFT. - -<pre class="example"> #include <fftw3-mpi.h> - - int main(int argc, char **argv) - { - const ptrdiff_t N0 = ..., N1 = ...; - fftw_plan plan; - fftw_complex *data; - ptrdiff_t alloc_local, local_n0, local_0_start, i, j; - - MPI_Init(&argc, &argv); - fftw_mpi_init(); - - /* <span class="roman">get local data size and allocate</span> */ - alloc_local = fftw3_mpi_local_size_2d(N0, N1, MPI_COMM_WORLD, - &local_n0, &local_0_start); - data = (fftw_complex *) fftw_malloc(sizeof(fftw_complex) * alloc_local); - - /* <span class="roman">create plan for forward DFT</span> */ - plan = fftw_mpi_plan_dft_2d(N0, N1, data, data, MPI_COMM_WORLD, - FFTW_FORWARD, FFTW_ESTIMATE); - - /* <span class="roman">initialize data to some function</span> my_function(x,y) */ - for (i = 0; i < local_n0; ++i) for (j = 0; j < N1; ++j) - data[i*N1 + j] = my_function(local_0_start + i, j); - - /* <span class="roman">compute transforms, in-place, as many times as desired</span> */ - fftw_execute(plan); - - fftw_destroy_plan(plan); - - MPI_Finalize(); - } -</pre> - <p>As can be seen above, the MPI interface follows the same basic style -of allocate/plan/execute/destroy as the serial FFTW routines. All of -the MPI-specific routines are prefixed with `<samp><span class="samp">fftw_mpi_</span></samp>' instead -of `<samp><span class="samp">fftw_</span></samp>'. There are a few important differences, however: - - <p>First, we must call <code>fftw_mpi_init()</code> after calling -<code>MPI_Init</code> (required in all MPI programs) and before calling any -other `<samp><span class="samp">fftw_mpi_</span></samp>' routine. -<a name="index-MPI_005fInit-340"></a><a name="index-fftw_005fmpi_005finit-341"></a> -Second, when we create the plan with <code>fftw_mpi_plan_dft_2d</code>, -analogous to <code>fftw_plan_dft_2d</code>, we pass an additional argument: -the communicator, indicating which processes will participate in the -transform (here <code>MPI_COMM_WORLD</code>, indicating all processes). -Whenever you create, execute, or destroy a plan for an MPI transform, -you must call the corresponding FFTW routine on <em>all</em> processes -in the communicator for that transform. (That is, these are -<em>collective</em> calls.) Note that the plan for the MPI transform -uses the standard <code>fftw_execute</code> and <code>fftw_destroy</code> -routines (the new-array execute routines also work). -<a name="index-collective-function-342"></a><a name="index-fftw_005fmpi_005fplan_005fdft_005f2d-343"></a><a name="index-MPI_005fCOMM_005fWORLD-344"></a> -Third, all of the FFTW MPI routines take <code>ptrdiff_t</code> arguments -instead of <code>int</code> as for the serial FFTW. <code>ptrdiff_t</code> is a -standard C integer type which is (at least) 32 bits wide on a 32-bit -machine and 64 bits wide on a 64-bit machine. This is to make it easy -to specify very large parallel transforms on a 64-bit machine. (You -can specify 64-bit transform sizes in the serial FFTW, too, but only -by using the `<samp><span class="samp">guru64</span></samp>' planner interface. See <a href="64_002dbit-Guru-Interface.html#g_t64_002dbit-Guru-Interface">64-bit Guru Interface</a>.) -<a name="index-ptrdiff_005ft-345"></a><a name="index-g_t64_002dbit-architecture-346"></a> -Fourth, and most importantly, you don't allocate the entire -two-dimensional array on each process. Instead, you call -<code>fftw_mpi_local_size_2d</code> to find out what <code>portion</code> of the -array resides on each processor, and how much space to allocate. -Here, the portion of the array on each process is a <code>local_n0</code> by -<code>N1</code> slice of the total array, starting at index -<code>local_0_start</code>. The total number of <code>fftw_complex</code> numbers -to allocate is given by the <code>alloc_local</code> return value, which -<em>may</em> be greater than <code>local_n0 * N1</code> (in case some -intermediate calculations require additional storage). The data -distribution in FFTW's MPI interface is described in more detail by -the next section. -<a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-347"></a><a name="index-data-distribution-348"></a> -Given the portion of the array that resides on the local process, it -is straightforward to initialize the data (here to a function -<code>myfunction</code>) and otherwise manipulate it. Of course, at the end -of the program you may want to output the data somehow, but -synchronizing this output is up to you and is beyond the scope of this -manual. (One good way to output a large multi-dimensional distributed -array in MPI to a portable binary file is to use the free HDF5 -library; see the <a href="http://www.hdfgroup.org/">HDF home page</a>.) -<a name="index-HDF5-349"></a> -<!-- --> - - </body></html> -