mirror of
https://github.com/tildearrow/furnace.git
synced 2024-12-02 09:17:26 +00:00
226 lines
11 KiB
HTML
226 lines
11 KiB
HTML
<!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.
|
|
|
|
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. -->
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>FFTW MPI Fortran Interface (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="FFTW MPI Fortran Interface (FFTW 3.3.10)">
|
|
<meta name="keywords" content="FFTW MPI Fortran Interface (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Distributed_002dmemory-FFTW-with-MPI.html" rel="up" title="Distributed-memory FFTW with MPI">
|
|
<link href="Calling-FFTW-from-Modern-Fortran.html" rel="next" title="Calling FFTW from Modern Fortran">
|
|
<link href="MPI-Wisdom-Communication.html" rel="prev" title="MPI Wisdom Communication">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="FFTW-MPI-Fortran-Interface"></span><div class="header">
|
|
<p>
|
|
Previous: <a href="FFTW-MPI-Reference.html" accesskey="p" rel="prev">FFTW MPI Reference</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</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>
|
|
<hr>
|
|
<span id="FFTW-MPI-Fortran-Interface-1"></span><h3 class="section">6.13 FFTW MPI Fortran Interface</h3>
|
|
<span id="index-Fortran-interface-1"></span>
|
|
|
|
<span id="index-iso_005fc_005fbinding"></span>
|
|
<p>The FFTW MPI interface is callable from modern Fortran compilers
|
|
supporting the Fortran 2003 <code>iso_c_binding</code> standard for calling
|
|
C functions. As described in <a href="Calling-FFTW-from-Modern-Fortran.html">Calling FFTW from Modern Fortran</a>,
|
|
this means that you can directly call FFTW’s C interface from Fortran
|
|
with only minor changes in syntax. There are, however, a few things
|
|
specific to the MPI interface to keep in mind:
|
|
</p>
|
|
<ul>
|
|
<li> Instead of including <code>fftw3.f03</code> as in <a href="Overview-of-Fortran-interface.html">Overview of Fortran interface</a>, you should <code>include 'fftw3-mpi.f03'</code> (after
|
|
<code>use, intrinsic :: iso_c_binding</code> as before). The
|
|
<code>fftw3-mpi.f03</code> file includes <code>fftw3.f03</code>, so you should
|
|
<em>not</em> <code>include</code> them both yourself. (You will also want to
|
|
include the MPI header file, usually via <code>include 'mpif.h'</code> or
|
|
similar, although though this is not needed by <code>fftw3-mpi.f03</code>
|
|
<i>per se</i>.) (To use the ‘<samp>fftwl_</samp>’ <code>long double</code> extended-precision routines in supporting compilers, you should include <code>fftw3f-mpi.f03</code> in <em>addition</em> to <code>fftw3-mpi.f03</code>. See <a href="Extended-and-quadruple-precision-in-Fortran.html">Extended and quadruple precision in Fortran</a>.)
|
|
|
|
</li><li> Because of the different storage conventions between C and Fortran,
|
|
you reverse the order of your array dimensions when passing them to
|
|
FFTW (see <a href="Reversing-array-dimensions.html">Reversing array dimensions</a>). This is merely a
|
|
difference in notation and incurs no performance overhead. However,
|
|
it means that, whereas in C the <em>first</em> dimension is distributed,
|
|
in Fortran the <em>last</em> dimension of your array is distributed.
|
|
|
|
</li><li> <span id="index-MPI-communicator-3"></span>
|
|
In Fortran, communicators are stored as <code>integer</code> types; there is
|
|
no <code>MPI_Comm</code> type, nor is there any way to access a C
|
|
<code>MPI_Comm</code>. Fortunately, this is taken care of for you by the
|
|
FFTW Fortran interface: whenever the C interface expects an
|
|
<code>MPI_Comm</code> type, you should pass the Fortran communicator as an
|
|
<code>integer</code>.<a id="DOCF8" href="#FOOT8"><sup>8</sup></a>
|
|
|
|
</li><li> Because you need to call the ‘<samp>local_size</samp>’ function to find out
|
|
how much space to allocate, and this may be <em>larger</em> than the
|
|
local portion of the array (see <a href="MPI-Data-Distribution.html">MPI Data Distribution</a>), you should
|
|
<em>always</em> allocate your arrays dynamically using FFTW’s allocation
|
|
routines as described in <a href="Allocating-aligned-memory-in-Fortran.html">Allocating aligned memory in Fortran</a>.
|
|
(Coincidentally, this also provides the best performance by
|
|
guaranteeding proper data alignment.)
|
|
|
|
</li><li> Because all sizes in the MPI FFTW interface are declared as
|
|
<code>ptrdiff_t</code> in C, you should use <code>integer(C_INTPTR_T)</code> in
|
|
Fortran (see <a href="FFTW-Fortran-type-reference.html">FFTW Fortran type reference</a>).
|
|
|
|
</li><li> <span id="index-fftw_005fexecute_005fdft-1"></span>
|
|
<span id="index-fftw_005fmpi_005fexecute_005fdft-1"></span>
|
|
<span id="index-new_002darray-execution-3"></span>
|
|
In Fortran, because of the language semantics, we generally recommend
|
|
using the new-array execute functions for all plans, even in the
|
|
common case where you are executing the plan on the same arrays for
|
|
which the plan was created (see <a href="Plan-execution-in-Fortran.html">Plan execution in Fortran</a>).
|
|
However, note that in the MPI interface these functions are changed:
|
|
<code>fftw_execute_dft</code> becomes <code>fftw_mpi_execute_dft</code>,
|
|
etcetera. See <a href="Using-MPI-Plans.html">Using MPI Plans</a>.
|
|
|
|
</li></ul>
|
|
|
|
<p>For example, here is a Fortran code snippet to perform a distributed
|
|
L × M
|
|
complex DFT in-place. (This assumes you have already
|
|
initialized MPI with <code>MPI_init</code> and have also performed
|
|
<code>call fftw_mpi_init</code>.)
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example"> use, intrinsic :: iso_c_binding
|
|
include 'fftw3-mpi.f03'
|
|
integer(C_INTPTR_T), parameter :: L = ...
|
|
integer(C_INTPTR_T), parameter :: M = ...
|
|
type(C_PTR) :: plan, cdata
|
|
complex(C_DOUBLE_COMPLEX), pointer :: data(:,:)
|
|
integer(C_INTPTR_T) :: i, j, alloc_local, local_M, local_j_offset
|
|
|
|
! <span class="roman">get local data size and allocate (note dimension reversal)</span>
|
|
alloc_local = fftw_mpi_local_size_2d(M, L, MPI_COMM_WORLD, &
|
|
local_M, local_j_offset)
|
|
cdata = fftw_alloc_complex(alloc_local)
|
|
call c_f_pointer(cdata, data, [L,local_M])
|
|
|
|
! <span class="roman">create MPI plan for in-place forward DFT (note dimension reversal)</span>
|
|
plan = fftw_mpi_plan_dft_2d(M, L, data, data, MPI_COMM_WORLD, &
|
|
FFTW_FORWARD, FFTW_MEASURE)
|
|
|
|
! <span class="roman">initialize data to some function</span> my_function(i,j)
|
|
do j = 1, local_M
|
|
do i = 1, L
|
|
data(i, j) = my_function(i, j + local_j_offset)
|
|
end do
|
|
end do
|
|
|
|
! <span class="roman">compute transform (as many times as desired)</span>
|
|
call fftw_mpi_execute_dft(plan, data, data)
|
|
|
|
call fftw_destroy_plan(plan)
|
|
call fftw_free(cdata)
|
|
</pre></div>
|
|
|
|
<p>Note that when we called <code>fftw_mpi_local_size_2d</code> and
|
|
<code>fftw_mpi_plan_dft_2d</code> with the dimensions in reversed order,
|
|
since a L × M
|
|
Fortran array is viewed by FFTW in C as a
|
|
M × L
|
|
array. This means that the array was distributed over
|
|
the <code>M</code> dimension, the local portion of which is a
|
|
L × local_M
|
|
array in Fortran. (You must <em>not</em> use an
|
|
<code>allocate</code> statement to allocate an L × local_M
|
|
array,
|
|
however; you must allocate <code>alloc_local</code> complex numbers, which
|
|
may be greater than <code>L * local_M</code>, in order to reserve space for
|
|
intermediate steps of the transform.) Finally, we mention that
|
|
because C’s array indices are zero-based, the <code>local_j_offset</code>
|
|
argument can conveniently be interpreted as an offset in the 1-based
|
|
<code>j</code> index (rather than as a starting index as in C).
|
|
</p>
|
|
<p>If instead you had used the <code>ior(FFTW_MEASURE,
|
|
FFTW_MPI_TRANSPOSED_OUT)</code> flag, the output of the transform would be a
|
|
transposed M × local_L
|
|
array, associated with the <em>same</em>
|
|
<code>cdata</code> allocation (since the transform is in-place), and which
|
|
you could declare with:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example"> complex(C_DOUBLE_COMPLEX), pointer :: tdata(:,:)
|
|
...
|
|
call c_f_pointer(cdata, tdata, [M,local_L])
|
|
</pre></div>
|
|
|
|
<p>where <code>local_L</code> would have been obtained by changing the
|
|
<code>fftw_mpi_local_size_2d</code> call to:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example"> alloc_local = fftw_mpi_local_size_2d_transposed(M, L, MPI_COMM_WORLD, &
|
|
local_M, local_j_offset, local_L, local_i_offset)
|
|
</pre></div>
|
|
<div class="footnote">
|
|
<hr>
|
|
<h4 class="footnotes-heading">Footnotes</h4>
|
|
|
|
<h5><a id="FOOT8" href="#DOCF8">(8)</a></h3>
|
|
<p>Technically, this is because you aren’t
|
|
actually calling the C functions directly. You are calling wrapper
|
|
functions that translate the communicator with <code>MPI_Comm_f2c</code>
|
|
before calling the ordinary C interface. This is all done
|
|
transparently, however, since the <code>fftw3-mpi.f03</code> interface file
|
|
renames the wrappers so that they are called in Fortran with the same
|
|
names as the C interface functions.</p>
|
|
</div>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Previous: <a href="FFTW-MPI-Reference.html" accesskey="p" rel="prev">FFTW MPI Reference</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</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>
|