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Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<!-- This manual is for FFTW
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+Copyright (C) 2003 Matteo Frigo.
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+<title>FFTW 3.3.5: Basic distributed-transpose interface</title>
+
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+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" rel="up" title="FFTW MPI Transposes">
+<link href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" rel="next" title="Advanced distributed-transpose interface">
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+<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
+<a name="Basic-distributed_002dtranspose-interface"></a>
+<div class="header">
+<p>
+Next: <a href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" accesskey="n" rel="next">Advanced distributed-transpose interface</a>, Previous: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="p" rel="prev">FFTW MPI Transposes</a>, Up: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="u" rel="up">FFTW MPI Transposes</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
+</div>
+<hr>
+<a name="Basic-distributed_002dtranspose-interface-1"></a>
+<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:
+</p>
+<div class="example">
+<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></div>
+<a name="index-fftw_005fmpi_005fplan_005ftranspose"></a>
+
+<p>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-3"></a>
+</p>
+
+<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-1"></a>
+<a name="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-1"></a>
+</p>
+
+<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-4"></a>
+</p>
+<div class="example">
+<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></div>
+<a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed"></a>
+
+<p>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.
+</p>
+<hr>
+<div class="header">
+<p>
+Next: <a href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" accesskey="n" rel="next">Advanced distributed-transpose interface</a>, Previous: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="p" rel="prev">FFTW MPI Transposes</a>, Up: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="u" rel="up">FFTW MPI Transposes</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
+</div>
+
+
+
+</body>
+</html>