Mercurial > hg > batch-feature-extraction-tool
diff Lib/fftw-3.2.1/doc/html/.svn/text-base/MPI-data-distribution.html.svn-base @ 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/.svn/text-base/MPI-data-distribution.html.svn-base Wed May 04 11:02:59 2016 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,101 +0,0 @@ -<html lang="en"> -<head> -<title>MPI data distribution - 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="Simple-MPI-example.html#Simple-MPI-example" title="Simple MPI example"> -<link rel="next" href="Multi_002ddimensional-MPI-DFT-of-Real-Data.html#Multi_002ddimensional-MPI-DFT-of-Real-Data" title="Multi-dimensional MPI DFT of Real Data"> -<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="MPI-data-distribution"></a> -Next: <a rel="next" accesskey="n" href="Multi_002ddimensional-MPI-DFT-of-Real-Data.html#Multi_002ddimensional-MPI-DFT-of-Real-Data">Multi-dimensional MPI DFT of Real Data</a>, -Previous: <a rel="previous" accesskey="p" href="Simple-MPI-example.html#Simple-MPI-example">Simple MPI example</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">6.4 MPI data distribution</h3> - -<p><a name="index-data-distribution-350"></a> -The most important concept to understand in using FFTW's MPI interface -is the data distribution. With a serial or multithreaded FFT, all of -the input and outputs are stored as a single contiguous chunk of -memory. With a distributed-memory FFT, the inputs and outputs are -broken into disjoint blocks, one per process. - - <p>In particular, FFTW uses a <em>1d block distribution</em> of the data, -distributed along the <em>first dimension</em>. For example, if you -want to perform a 100 × 200 complex DFT, distributed over 4 -processes, each process will get a 25 × 200 slice of the data. -That is, process 0 will get rows 0 through 24, process 1 will get rows -25 through 49, process 2 will get rows 50 through 74, and process 3 -will get rows 75 through 99. If you take the same array but -distribute it over 3 processes, then it is not evenly divisible so the -different processes will have unequal chunks. FFTW's default choice -in this case is to assign 34 rows to processes 0 and 1, and 32 rows to -process 2. -<a name="index-block-distribution-351"></a> -FFTW provides several `<samp><span class="samp">fftw_mpi_local_size</span></samp>' routines that you can -call to find out what portion of an array is stored on the current -process. In most cases, you should use the default block sizes picked -by FFTW, but it is also possible to specify your own block size. For -example, with a 100 × 200 array on three processes, you can -tell FFTW to use a block size of 40, which would assign 40 rows to -processes 0 and 1, and 20 rows to process 2. FFTW's default is to -divide the data equally among the processes if possible, and as best -it can otherwise. The rows are always assigned in “rank order,” -i.e. process 0 gets the first block of rows, then process 1, and so -on. (You can change this by using <code>MPI_Comm_split</code> to create a -new communicator with re-ordered processes.) However, you should -always call the `<samp><span class="samp">fftw_mpi_local_size</span></samp>' routines, if possible, -rather than trying to predict FFTW's distribution choices. - -<ul class="menu"> -<li><a accesskey="1" href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a> -<li><a accesskey="2" href="Load-balancing.html#Load-balancing">Load balancing</a> -<li><a accesskey="3" href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a> -<li><a accesskey="4" href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a> -</ul> - - </body></html> -