<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- This manual is for FFTW (version 3.3.10, 10 December 2020). 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. 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The <code>comm</code> argument gives an MPI communicator that specifies the set of processes to participate in the transform; plan creation is a collective function that must be called for all processes in the communicator. The <code>in</code> and <code>out</code> pointers refer only to a portion of the overall transform data (see <a href="MPI-Data-Distribution.html">MPI Data Distribution</a>) as specified by the ‘<samp>local_size</samp>’ functions in the previous section. Unless <code>flags</code> contains <code>FFTW_ESTIMATE</code>, these arrays are overwritten during plan creation as for the serial interface. For multi-dimensional transforms, any dimensions <code>> 1</code> are supported; for one-dimensional transforms, only composite (non-prime) <code>n0</code> are currently supported (unlike the serial FFTW). Requesting an unsupported transform size will yield a <code>NULL</code> plan. (As in the serial interface, highly composite sizes generally yield the best performance.) </p> <span id="index-advanced-interface-6"></span> <span id="index-FFTW_005fMPI_005fDEFAULT_005fBLOCK-2"></span> <span id="index-stride-3"></span> <p>The advanced-interface <code>fftw_mpi_plan_many_dft</code> additionally allows you to specify the block sizes for the first dimension (<code>block</code>) of the n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub> input data and the first dimension (<code>tblock</code>) of the n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> transposed data (at intermediate steps of the transform, and for the output if <code>FFTW_TRANSPOSED_OUT</code> is specified in <code>flags</code>). These must be the same block sizes as were passed to the corresponding ‘<samp>local_size</samp>’ function; you can pass <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW’s default block size as in the basic interface. Also, the <code>howmany</code> parameter specifies that the transform is of contiguous <code>howmany</code>-tuples rather than individual complex numbers; this corresponds to the same parameter in the serial advanced interface (see <a href="Advanced-Complex-DFTs.html">Advanced Complex DFTs</a>) with <code>stride = howmany</code> and <code>dist = 1</code>. </p> <span id="MPI-flags"></span><h4 class="subsubheading">MPI flags</h4> <p>The <code>flags</code> can be any of those for the serial FFTW (see <a href="Planner-Flags.html">Planner Flags</a>), and in addition may include one or more of the following MPI-specific flags, which improve performance at the cost of changing the output or input data formats. </p> <ul> <li> <span id="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-2"></span> <span id="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-2"></span> <code>FFTW_MPI_SCRAMBLED_OUT</code>, <code>FFTW_MPI_SCRAMBLED_IN</code>: valid for 1d transforms only, these flags indicate that the output/input of the transform are in an undocumented “scrambled” order. A forward <code>FFTW_MPI_SCRAMBLED_OUT</code> transform can be inverted by a backward <code>FFTW_MPI_SCRAMBLED_IN</code> (times the usual 1/<i>N</i> normalization). See <a href="One_002ddimensional-distributions.html">One-dimensional distributions</a>. </li><li> <span id="index-FFTW_005fMPI_005fTRANSPOSED_005fOUT-2"></span> <span id="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-2"></span> <code>FFTW_MPI_TRANSPOSED_OUT</code>, <code>FFTW_MPI_TRANSPOSED_IN</code>: valid for multidimensional (<code>rnk > 1</code>) transforms only, these flags specify that the output or input of an n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub> transform is transposed to n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> . See <a href="Transposed-distributions.html">Transposed distributions</a>. </li></ul> <span id="Real_002ddata-MPI-DFTs"></span><h4 class="subsubheading">Real-data MPI DFTs</h4> <span id="index-r2c-4"></span> <p>Plans for real-input/output (r2c/c2r) DFTs (see <a href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html">Multi-dimensional MPI DFTs of Real Data</a>) are created by: </p> <span id="index-fftw_005fmpi_005fplan_005fdft_005fr2c_005f2d"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fr2c_005f2d-1"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fr2c_005f3d"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fr2c"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fc2r_005f2d"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fc2r_005f2d-1"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fc2r_005f3d"></span> <span id="index-fftw_005fmpi_005fplan_005fdft_005fc2r"></span> <div class="example"> <pre class="example">fftw_plan fftw_mpi_plan_dft_r2c_2d(ptrdiff_t n0, ptrdiff_t n1, double *in, fftw_complex *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_r2c_2d(ptrdiff_t n0, ptrdiff_t n1, double *in, fftw_complex *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_r2c_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, double *in, fftw_complex *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_r2c(int rnk, const ptrdiff_t *n, double *in, fftw_complex *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_c2r_2d(ptrdiff_t n0, ptrdiff_t n1, fftw_complex *in, double *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_c2r_2d(ptrdiff_t n0, ptrdiff_t n1, fftw_complex *in, double *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_c2r_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, fftw_complex *in, double *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_dft_c2r(int rnk, const ptrdiff_t *n, fftw_complex *in, double *out, MPI_Comm comm, unsigned flags); </pre></div> <p>Similar to the serial interface (see <a href="Real_002ddata-DFTs.html">Real-data DFTs</a>), these transform logically n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub> real data to/from n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × (n<sub>d-1</sub>/2 + 1) complex data, representing the non-redundant half of the conjugate-symmetry output of a real-input DFT (see <a href="Multi_002ddimensional-Transforms.html">Multi-dimensional Transforms</a>). However, the real array must be stored within a padded n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × [2 (n<sub>d-1</sub>/2 + 1)] array (much like the in-place serial r2c transforms, but here for out-of-place transforms as well). Currently, only multi-dimensional (<code>rnk > 1</code>) r2c/c2r transforms are supported (requesting a plan for <code>rnk = 1</code> will yield <code>NULL</code>). As explained above (see <a href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html">Multi-dimensional MPI DFTs of Real Data</a>), the data distribution of both the real and complex arrays is given by the ‘<samp>local_size</samp>’ function called for the dimensions of the <em>complex</em> array. Similar to the other planning functions, the input and output arrays are overwritten when the plan is created except in <code>FFTW_ESTIMATE</code> mode. </p> <p>As for the complex DFTs above, there is an advance interface that allows you to manually specify block sizes and to transform contiguous <code>howmany</code>-tuples of real/complex numbers: </p> <span id="index-fftw_005fmpi_005fplan_005fmany_005fdft_005fr2c"></span> <span id="index-fftw_005fmpi_005fplan_005fmany_005fdft_005fc2r"></span> <div class="example"> <pre class="example">fftw_plan fftw_mpi_plan_many_dft_r2c (int rnk, const ptrdiff_t *n, ptrdiff_t howmany, ptrdiff_t iblock, ptrdiff_t oblock, double *in, fftw_complex *out, MPI_Comm comm, unsigned flags); fftw_plan fftw_mpi_plan_many_dft_c2r (int rnk, const ptrdiff_t *n, ptrdiff_t howmany, ptrdiff_t iblock, ptrdiff_t oblock, fftw_complex *in, double *out, MPI_Comm comm, unsigned flags); </pre></div> <span id="MPI-r2r-transforms"></span><h4 class="subsubheading">MPI r2r transforms</h4> <span id="index-r2r-4"></span> <p>There are corresponding plan-creation routines for r2r transforms (see <a href="More-DFTs-of-Real-Data.html">More DFTs of Real Data</a>), currently supporting multidimensional (<code>rnk > 1</code>) transforms only (<code>rnk = 1</code> will yield a <code>NULL</code> plan): </p> <div class="example"> <pre class="example">fftw_plan fftw_mpi_plan_r2r_2d(ptrdiff_t n0, ptrdiff_t n1, double *in, double *out, MPI_Comm comm, fftw_r2r_kind kind0, fftw_r2r_kind kind1, unsigned flags); fftw_plan fftw_mpi_plan_r2r_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, double *in, double *out, MPI_Comm comm, fftw_r2r_kind kind0, fftw_r2r_kind kind1, fftw_r2r_kind kind2, unsigned flags); fftw_plan fftw_mpi_plan_r2r(int rnk, const ptrdiff_t *n, double *in, double *out, MPI_Comm comm, const fftw_r2r_kind *kind, unsigned flags); fftw_plan fftw_mpi_plan_many_r2r(int rnk, const ptrdiff_t *n, ptrdiff_t iblock, ptrdiff_t oblock, double *in, double *out, MPI_Comm comm, const fftw_r2r_kind *kind, unsigned flags); </pre></div> <p>The parameters are much the same as for the complex DFTs above, except that the arrays are of real numbers (and hence the outputs of the ‘<samp>local_size</samp>’ data-distribution functions should be interpreted as counts of real rather than complex numbers). Also, the <code>kind</code> parameters specify the r2r kinds along each dimension as for the serial interface (see <a href="Real_002dto_002dReal-Transform-Kinds.html">Real-to-Real Transform Kinds</a>). See <a href="Other-Multi_002ddimensional-Real_002ddata-MPI-Transforms.html">Other Multi-dimensional Real-data MPI Transforms</a>. </p> <span id="MPI-transposition"></span><h4 class="subsubheading">MPI transposition</h4> <span id="index-transpose-5"></span> <p>FFTW also provides routines to plan a transpose of a distributed <code>n0</code> by <code>n1</code> array of real numbers, or an array of <code>howmany</code>-tuples of real numbers with specified block sizes (see <a href="FFTW-MPI-Transposes.html">FFTW MPI Transposes</a>): </p> <span id="index-fftw_005fmpi_005fplan_005ftranspose-1"></span> <span id="index-fftw_005fmpi_005fplan_005fmany_005ftranspose-1"></span> <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); fftw_plan fftw_mpi_plan_many_transpose (ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t howmany, ptrdiff_t block0, ptrdiff_t block1, double *in, double *out, MPI_Comm comm, unsigned flags); </pre></div> <span id="index-new_002darray-execution-2"></span> <span id="index-fftw_005fmpi_005fexecute_005fr2r-1"></span> <p>These plans are used with the <code>fftw_mpi_execute_r2r</code> new-array execute function (see <a href="Using-MPI-Plans.html">Using MPI Plans</a>), since they count as (rank zero) r2r plans from FFTW’s perspective. </p> <hr> <div class="header"> <p> Next: <a href="MPI-Wisdom-Communication.html" accesskey="n" rel="next">MPI Wisdom Communication</a>, Previous: <a href="MPI-Data-Distribution-Functions.html" accesskey="p" rel="prev">MPI Data Distribution Functions</a>, Up: <a href="FFTW-MPI-Reference.html" accesskey="u" rel="up">FFTW MPI Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p> </div> </body> </html>