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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents 37bf6b4a2645
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Chris@10 1 <html lang="en">
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Chris@10 3 <title>Basic distributed-transpose interface - FFTW 3.3.3</title>
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Chris@10 48 <div class="node">
Chris@10 49 <a name="Basic-distributed-transpose-interface"></a>
Chris@10 50 <a name="Basic-distributed_002dtranspose-interface"></a>
Chris@10 51 <p>
Chris@10 52 Next:&nbsp;<a rel="next" accesskey="n" href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface">Advanced distributed-transpose interface</a>,
Chris@10 53 Previous:&nbsp;<a rel="previous" accesskey="p" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a>,
Chris@10 54 Up:&nbsp;<a rel="up" accesskey="u" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a>
Chris@10 55 <hr>
Chris@10 56 </div>
Chris@10 57
Chris@10 58 <h4 class="subsection">6.7.1 Basic distributed-transpose interface</h4>
Chris@10 59
Chris@10 60 <p>In particular, suppose that we have an <code>n0</code> by <code>n1</code> array in
Chris@10 61 row-major order, block-distributed across the <code>n0</code> dimension. To
Chris@10 62 transpose this into an <code>n1</code> by <code>n0</code> array block-distributed
Chris@10 63 across the <code>n1</code> dimension, we would create a plan by calling the
Chris@10 64 following function:
Chris@10 65
Chris@10 66 <pre class="example"> fftw_plan fftw_mpi_plan_transpose(ptrdiff_t n0, ptrdiff_t n1,
Chris@10 67 double *in, double *out,
Chris@10 68 MPI_Comm comm, unsigned flags);
Chris@10 69 </pre>
Chris@10 70 <p><a name="index-fftw_005fmpi_005fplan_005ftranspose-397"></a>
Chris@10 71 The input and output arrays (<code>in</code> and <code>out</code>) can be the
Chris@10 72 same. The transpose is actually executed by calling
Chris@10 73 <code>fftw_execute</code> on the plan, as usual.
Chris@10 74 <a name="index-fftw_005fexecute-398"></a>
Chris@10 75
Chris@10 76 <p>The <code>flags</code> are the usual FFTW planner flags, but support
Chris@10 77 two additional flags: <code>FFTW_MPI_TRANSPOSED_OUT</code> and/or
Chris@10 78 <code>FFTW_MPI_TRANSPOSED_IN</code>. What these flags indicate, for
Chris@10 79 transpose plans, is that the output and/or input, respectively, are
Chris@10 80 <em>locally</em> transposed. That is, on each process input data is
Chris@10 81 normally stored as a <code>local_n0</code> by <code>n1</code> array in row-major
Chris@10 82 order, but for an <code>FFTW_MPI_TRANSPOSED_IN</code> plan the input data is
Chris@10 83 stored as <code>n1</code> by <code>local_n0</code> in row-major order. Similarly,
Chris@10 84 <code>FFTW_MPI_TRANSPOSED_OUT</code> means that the output is <code>n0</code> by
Chris@10 85 <code>local_n1</code> instead of <code>local_n1</code> by <code>n0</code>.
Chris@10 86 <a name="index-FFTW_005fMPI_005fTRANSPOSED_005fOUT-399"></a><a name="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-400"></a>
Chris@10 87
Chris@10 88 <p>To determine the local size of the array on each process before and
Chris@10 89 after the transpose, as well as the amount of storage that must be
Chris@10 90 allocated, one should call <code>fftw_mpi_local_size_2d_transposed</code>,
Chris@10 91 just as for a 2d DFT as described in the previous section:
Chris@10 92 <a name="index-data-distribution-401"></a>
Chris@10 93 <pre class="example"> ptrdiff_t fftw_mpi_local_size_2d_transposed
Chris@10 94 (ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
Chris@10 95 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
Chris@10 96 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
Chris@10 97 </pre>
Chris@10 98 <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-402"></a>
Chris@10 99 Again, the return value is the local storage to allocate, which in
Chris@10 100 this case is the number of <em>real</em> (<code>double</code>) values rather
Chris@10 101 than complex numbers as in the previous examples.
Chris@10 102
Chris@10 103 </body></html>
Chris@10 104