Mercurial > hg > batch-feature-extraction-tool
diff Lib/fftw-3.2.1/doc/html/.svn/text-base/Transposed-distributions.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/Transposed-distributions.html.svn-base Wed May 04 11:02:59 2016 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,127 +0,0 @@ -<html lang="en"> -<head> -<title>Transposed distributions - 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="Load-balancing.html#Load-balancing" title="Load balancing"> -<link rel="next" href="One_002ddimensional-distributions.html#One_002ddimensional-distributions" title="One-dimensional distributions"> -<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="Transposed-distributions"></a> -Next: <a rel="next" accesskey="n" href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>, -Previous: <a rel="previous" accesskey="p" href="Load-balancing.html#Load-balancing">Load balancing</a>, -Up: <a rel="up" accesskey="u" href="MPI-data-distribution.html#MPI-data-distribution">MPI data distribution</a> -<hr> -</div> - -<h4 class="subsection">6.4.3 Transposed distributions</h4> - -<p>Internally, FFTW's MPI transform algorithms work by first computing -transforms of the data local to each process, then by globally -<em>transposing</em> the data in some fashion to redistribute the data -among the processes, transforming the new data local to each process, -and transposing back. For example, a two-dimensional <code>n0</code> by -<code>n1</code> array, distributed across the <code>n0</code> dimension, is -transformd by: (i) transforming the <code>n1</code> dimension, which are -local to each process; (ii) transposing to a <code>n1</code> by <code>n0</code> -array, distributed across the <code>n1</code> dimension; (iii) transforming -the <code>n0</code> dimension, which is now local to each process; (iv) -transposing back. -<a name="index-transpose-359"></a> -However, in many applications it is acceptable to compute a -multidimensional DFT whose results are produced in transposed order -(e.g., <code>n1</code> by <code>n0</code> in two dimensions). This provides a -significant performance advantage, because it means that the final -transposition step can be omitted. FFTW supports this optimization, -which you specify by passing the flag <code>FFTW_MPI_TRANSPOSED_OUT</code> -to the planner routines. To compute the inverse transform of -transposed output, you specify <code>FFTW_MPI_TRANSPOSED_IN</code> to tell -it that the input is transposed. In this section, we explain how to -interpret the output format of such a transform. -<a name="index-FFTW_005fMPI_005fTRANSPOSED_005fOUT-360"></a><a name="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-361"></a> -Suppose you have are transforming multi-dimensional data with (at -least two) dimensions n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub>. As always, it is distributed along -the first dimension n<sub>0</sub>. Now, if we compute its DFT with the -<code>FFTW_MPI_TRANSPOSED_OUT</code>, the resulting output data are stored -with the first <em>two</em> dimensions transosed: n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub>, -distributed along the n<sub>0</sub> dimension. Conversely, if we take the -n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> data and transform it with the -<code>FFTW_MPI_TRANSPOSED_IN</code> flag, then the format goes back to the -original n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub>. - - <p>There are two ways to find the portion of the transposed array that -resides on the current process. First, you can simply call the -appropriate `<samp><span class="samp">local_size</span></samp>' function, passing n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> (the -transposed dimensions). This would mean calling the `<samp><span class="samp">local_size</span></samp>' -function twice, once for the transposed and once for the -non-transposed dimensions. Alternatively, you can call one of the -`<samp><span class="samp">local_size_transposed</span></samp>' functions, which returns both the -non-transposed and transposed data distribution from a single call. -For example, for a 3d transform with transposed output (or input), you -might call: - -<pre class="example"> ptrdiff_t fftw_mpi_local_size_3d_transposed( - ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, MPI_Comm comm, - ptrdiff_t *local_n0, ptrdiff_t *local_0_start, - ptrdiff_t *local_n1, ptrdiff_t *local_1_start); -</pre> - <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-362"></a> -Here, <code>local_n0</code> and <code>local_0_start</code> give the size and -starting index of the <code>n0</code> dimension, for the -<em>non</em>-transposed data, as in the previous sections. For -<em>transposed</em> data (e.g. the output for -<code>FFTW_MPI_TRANSPOSED_OUT</code>), <code>local_n1</code> and -<code>local_1_start</code> give the size and starting index of the <code>n1</code> -dimension, which is the first dimension of the transposed data -(<code>n1</code> by <code>n0</code> by <code>n2</code>). - - <p>(Note that <code>FFTW_MPI_TRANSPOSED_IN</code> is completely equivalent to -performing <code>FFTW_MPI_TRANSPOSED_OUT</code> and passing the first two -dimensions to the planner in reverse order, or vice versa. If you -pass <em>both</em> the <code>FFTW_MPI_TRANSPOSED_IN</code> and -<code>FFTW_MPI_TRANSPOSED_OUT</code> flags, it is equivalent to swapping the -first two dimensions passed to the planner and passing <em>neither</em> -flag.) - - </body></html> -