cannam@95: <html lang="en"> cannam@95: <head> cannam@95: <title>Complex numbers - FFTW 3.3.3</title> cannam@95: <meta http-equiv="Content-Type" content="text/html"> cannam@95: <meta name="description" content="FFTW 3.3.3"> cannam@95: <meta name="generator" content="makeinfo 4.13"> cannam@95: <link title="Top" rel="start" href="index.html#Top"> cannam@95: <link rel="up" href="Data-Types-and-Files.html#Data-Types-and-Files" title="Data Types and Files"> cannam@95: <link rel="prev" href="Data-Types-and-Files.html#Data-Types-and-Files" title="Data Types and Files"> cannam@95: <link rel="next" href="Precision.html#Precision" title="Precision"> cannam@95: <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> cannam@95: <!-- cannam@95: This manual is for FFTW cannam@95: (version 3.3.3, 25 November 2012). cannam@95: cannam@95: Copyright (C) 2003 Matteo Frigo. cannam@95: cannam@95: Copyright (C) 2003 Massachusetts Institute of Technology. cannam@95: cannam@95: Permission is granted to make and distribute verbatim copies of cannam@95: this manual provided the copyright notice and this permission cannam@95: notice are preserved on all copies. cannam@95: cannam@95: Permission is granted to copy and distribute modified versions of cannam@95: this manual under the conditions for verbatim copying, provided cannam@95: that the entire resulting derived work is distributed under the cannam@95: terms of a permission notice identical to this one. cannam@95: cannam@95: Permission is granted to copy and distribute translations of this cannam@95: manual into another language, under the above conditions for cannam@95: modified versions, except that this permission notice may be cannam@95: stated in a translation approved by the Free Software Foundation. cannam@95: --> cannam@95: <meta http-equiv="Content-Style-Type" content="text/css"> cannam@95: <style type="text/css"><!-- cannam@95: pre.display { font-family:inherit } cannam@95: pre.format { font-family:inherit } cannam@95: pre.smalldisplay { font-family:inherit; font-size:smaller } cannam@95: pre.smallformat { font-family:inherit; font-size:smaller } cannam@95: pre.smallexample { font-size:smaller } cannam@95: pre.smalllisp { font-size:smaller } cannam@95: span.sc { font-variant:small-caps } cannam@95: span.roman { font-family:serif; font-weight:normal; } cannam@95: span.sansserif { font-family:sans-serif; font-weight:normal; } cannam@95: --></style> cannam@95: </head> cannam@95: <body> cannam@95: <div class="node"> cannam@95: <a name="Complex-numbers"></a> cannam@95: <p> cannam@95: Next: <a rel="next" accesskey="n" href="Precision.html#Precision">Precision</a>, cannam@95: Previous: <a rel="previous" accesskey="p" href="Data-Types-and-Files.html#Data-Types-and-Files">Data Types and Files</a>, cannam@95: Up: <a rel="up" accesskey="u" href="Data-Types-and-Files.html#Data-Types-and-Files">Data Types and Files</a> cannam@95: <hr> cannam@95: </div> cannam@95: cannam@95: <h4 class="subsection">4.1.1 Complex numbers</h4> cannam@95: cannam@95: <p>The default FFTW interface uses <code>double</code> precision for all cannam@95: floating-point numbers, and defines a <code>fftw_complex</code> type to hold cannam@95: complex numbers as: cannam@95: cannam@95: <pre class="example"> typedef double fftw_complex[2]; cannam@95: </pre> cannam@95: <p><a name="index-fftw_005fcomplex-139"></a> cannam@95: Here, the <code>[0]</code> element holds the real part and the <code>[1]</code> cannam@95: element holds the imaginary part. cannam@95: cannam@95: <p>Alternatively, if you have a C compiler (such as <code>gcc</code>) that cannam@95: supports the C99 revision of the ANSI C standard, you can use C's new cannam@95: native complex type (which is binary-compatible with the typedef above). cannam@95: In particular, if you <code>#include <complex.h></code> <em>before</em> cannam@95: <code><fftw3.h></code>, then <code>fftw_complex</code> is defined to be the native cannam@95: complex type and you can manipulate it with ordinary arithmetic cannam@95: (e.g. <code>x = y * (3+4*I)</code>, where <code>x</code> and <code>y</code> are cannam@95: <code>fftw_complex</code> and <code>I</code> is the standard symbol for the cannam@95: imaginary unit); cannam@95: <a name="index-C99-140"></a> cannam@95: cannam@95: <p>C++ has its own <code>complex<T></code> template class, defined in the cannam@95: standard <code><complex></code> header file. Reportedly, the C++ standards cannam@95: committee has recently agreed to mandate that the storage format used cannam@95: for this type be binary-compatible with the C99 type, i.e. an array cannam@95: <code>T[2]</code> with consecutive real <code>[0]</code> and imaginary <code>[1]</code> cannam@95: parts. (See report cannam@95: <a href="http://www.open-std.org/jtc1/sc22/WG21/docs/papers/2002/n1388.pdf WG21/N1388">http://www.open-std.org/jtc1/sc22/WG21/docs/papers/2002/n1388.pdf WG21/N1388</a>.) Although not part of the official standard as of this cannam@95: writing, the proposal stated that: “This solution has been tested with cannam@95: all current major implementations of the standard library and shown to cannam@95: be working.” To the extent that this is true, if you have a variable cannam@95: <code>complex<double> *x</code>, you can pass it directly to FFTW via cannam@95: <code>reinterpret_cast<fftw_complex*>(x)</code>. cannam@95: <a name="index-C_002b_002b-141"></a><a name="index-portability-142"></a> cannam@95: <!-- =========> --> cannam@95: cannam@95: </body></html> cannam@95: