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| author | Chris Cannam |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Basic-distributed_002dtranspose-interface.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,104 @@ +<html lang="en"> +<head> +<title>Basic distributed-transpose interface - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" title="FFTW MPI Transposes"> +<link rel="prev" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" title="FFTW MPI Transposes"> +<link rel="next" href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" title="Advanced distributed-transpose interface"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +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"> +<a name="Basic-distributed-transpose-interface"></a> +<a name="Basic-distributed_002dtranspose-interface"></a> +<p> +Next: <a rel="next" accesskey="n" href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface">Advanced distributed-transpose interface</a>, +Previous: <a rel="previous" accesskey="p" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a>, +Up: <a rel="up" accesskey="u" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a> +<hr> +</div> + +<h4 class="subsection">6.7.1 Basic distributed-transpose interface</h4> + +<p>In particular, suppose that we have an <code>n0</code> by <code>n1</code> array in +row-major order, block-distributed across the <code>n0</code> dimension. To +transpose this into an <code>n1</code> by <code>n0</code> array block-distributed +across the <code>n1</code> dimension, we would create a plan by calling the +following function: + +<pre class="example"> fftw_plan fftw_mpi_plan_transpose(ptrdiff_t n0, ptrdiff_t n1, + double *in, double *out, + MPI_Comm comm, unsigned flags); +</pre> + <p><a name="index-fftw_005fmpi_005fplan_005ftranspose-397"></a> +The input and output arrays (<code>in</code> and <code>out</code>) can be the +same. The transpose is actually executed by calling +<code>fftw_execute</code> on the plan, as usual. +<a name="index-fftw_005fexecute-398"></a> + + <p>The <code>flags</code> are the usual FFTW planner flags, but support +two additional flags: <code>FFTW_MPI_TRANSPOSED_OUT</code> and/or +<code>FFTW_MPI_TRANSPOSED_IN</code>. What these flags indicate, for +transpose plans, is that the output and/or input, respectively, are +<em>locally</em> transposed. That is, on each process input data is +normally stored as a <code>local_n0</code> by <code>n1</code> array in row-major +order, but for an <code>FFTW_MPI_TRANSPOSED_IN</code> plan the input data is +stored as <code>n1</code> by <code>local_n0</code> in row-major order. Similarly, +<code>FFTW_MPI_TRANSPOSED_OUT</code> means that the output is <code>n0</code> by +<code>local_n1</code> instead of <code>local_n1</code> by <code>n0</code>. +<a name="index-FFTW_005fMPI_005fTRANSPOSED_005fOUT-399"></a><a name="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-400"></a> + + <p>To determine the local size of the array on each process before and +after the transpose, as well as the amount of storage that must be +allocated, one should call <code>fftw_mpi_local_size_2d_transposed</code>, +just as for a 2d DFT as described in the previous section: +<a name="index-data-distribution-401"></a> +<pre class="example"> ptrdiff_t fftw_mpi_local_size_2d_transposed + (ptrdiff_t n0, ptrdiff_t n1, 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_005f2d_005ftransposed-402"></a> +Again, the return value is the local storage to allocate, which in +this case is the number of <em>real</em> (<code>double</code>) values rather +than complex numbers as in the previous examples. + + </body></html> +