Mercurial > hg > batch-feature-extraction-tool
diff Lib/fftw-3.2.1/doc/html/.svn/text-base/Basic-and-advanced-distribution-interfaces.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/Basic-and-advanced-distribution-interfaces.html.svn-base Wed May 04 11:02:59 2016 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,144 +0,0 @@ -<html lang="en"> -<head> -<title>Basic and advanced distribution interfaces - 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="MPI-data-distribution.html#MPI-data-distribution" title="MPI data distribution"> -<link rel="prev" href="MPI-data-distribution.html#MPI-data-distribution" title="MPI data distribution"> -<link rel="next" href="Load-balancing.html#Load-balancing" title="Load balancing"> -<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="Basic-and-advanced-distribution-interfaces"></a> -Next: <a rel="next" accesskey="n" href="Load-balancing.html#Load-balancing">Load balancing</a>, -Previous: <a rel="previous" accesskey="p" href="MPI-data-distribution.html#MPI-data-distribution">MPI data distribution</a>, -Up: <a rel="up" accesskey="u" href="MPI-data-distribution.html#MPI-data-distribution">MPI data distribution</a> -<hr> -</div> - -<h4 class="subsection">6.4.1 Basic and advanced distribution interfaces</h4> - -<p>As with the planner interface, the `<samp><span class="samp">fftw_mpi_local_size</span></samp>' -distribution interface is broken into basic and advanced -(`<samp><span class="samp">_many</span></samp>') interfaces, where the latter allows you to specify the -block size manually and also to request block sizes when computing -multiple transforms simultaneously. These functions are documented -more exhaustively by the FFTW MPI Reference, but we summarize the -basic ideas here using a couple of two-dimensional examples. - - <p>For the 100 × 200 complex-DFT example, above, we would find -the distribution by calling the following function in the basic -interface: - -<pre class="example"> ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm, - ptrdiff_t *local_n0, ptrdiff_t *local_0_start); -</pre> - <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-352"></a> -Given the total size of the data to be transformed (here, <code>n0 = -100</code> and <code>n1 = 200</code>) and an MPI communicator (<code>comm</code>), this -function provides three numbers. - - <p>First, it describes the shape of the local data: the current process -should store a <code>local_n0</code> by <code>n1</code> slice of the overall -dataset, in row-major order (<code>n1</code> dimension contiguous), starting -at index <code>local_0_start</code>. That is, if the total dataset is -viewed as a <code>n0</code> by <code>n1</code> matrix, the current process should -store the rows <code>local_0_start</code> to -<code>local_0_start+local_n0-1</code>. Obviously, if you are running with -only a single MPI process, that process will store the entire array: -<code>local_0_start</code> will be zero and <code>local_n0</code> will be -<code>n0</code>. See <a href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>. -<a name="index-row_002dmajor-353"></a> -Second, the return value is the total number of data elements (e.g., -complex numbers for a complex DFT) that should be allocated for the -input and output arrays on the current process (ideally with -<code>fftw_malloc</code>, to ensure optimal alignment). It might seem that -this should always be equal to <code>local_n0 * n1</code>, but this is -<em>not</em> the case. FFTW's distributed FFT algorithms require data -redistributions at intermediate stages of the transform, and in some -circumstances this may require slightly larger local storage. This is -discussed in more detail below, under <a href="Load-balancing.html#Load-balancing">Load balancing</a>. -<a name="index-fftw_005fmalloc-354"></a> -The advanced-interface `<samp><span class="samp">local_size</span></samp>' function for multidimensional -transforms returns the same three things (<code>local_n0</code>, -<code>local_0_start</code>, and the total number of elements to allocate), -but takes more inputs: - -<pre class="example"> ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, - ptrdiff_t howmany, - ptrdiff_t block0, - MPI_Comm comm, - ptrdiff_t *local_n0, - ptrdiff_t *local_0_start); -</pre> - <p><a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-355"></a> -The two-dimensional case above corresponds to <code>rnk = 2</code> and an -array <code>n</code> of length 2 with <code>n[0] = n0</code> and <code>n[1] = n1</code>. -This routine is for any <code>rnk > 1</code>; one-dimensional transforms -have their own interface because they work slightly differently, as -discussed below. - - <p>First, the advanced interface allows you to perform multiple -transforms at once, of interleaved data, as specified by the -<code>howmany</code> parameter. (<code>hoamany</code> is 1 for a single -transform.) - - <p>Second, here you can specify your desired block size in the <code>n0</code> -dimension, <code>block0</code>. To use FFTW's default block size, pass -<code>FFTW_MPI_DEFAULT_BLOCK</code> (0) for <code>block0</code>. Otherwise, on -<code>P</code> processes, FFTW will return <code>local_n0</code> equal to -<code>block0</code> on the first <code>P / block0</code> processes (rounded down), -return <code>local_n0</code> equal to <code>n0 - block0 * (P / block0)</code> on -the next process, and <code>local_n0</code> equal to zero on any remaining -processes. In general, we recommend using the default block size -(which corresponds to <code>n0 / P</code>, rounded up). -<a name="index-FFTW_005fMPI_005fDEFAULT_005fBLOCK-356"></a><a name="index-block-distribution-357"></a> -For example, suppose you have <code>P = 4</code> processes and <code>n0 = -21</code>. The default will be a block size of <code>6</code>, which will give -<code>local_n0 = 6</code> on the first three processes and <code>local_n0 = -3</code> on the last process. Instead, however, you could specify -<code>block0 = 5</code> if you wanted, which would give <code>local_n0 = 5</code> -on processes 0 to 2, <code>local_n0 = 6</code> on process 3. (This choice, -while it may look superficially more “balanced,” has the same -critical path as FFTW's default but requires more communications.) - - </body></html> -