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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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cannam@167 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
cannam@167 7
cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: Dynamic Arrays in C-The Wrong Way</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: Dynamic Arrays in C-The Wrong Way">
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cannam@167 36 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
cannam@167 37 <link href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans" rel="next" title="Words of Wisdom-Saving Plans">
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="Dynamic-Arrays-in-C_002dThe-Wrong-Way"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 74 Previous: <a href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" accesskey="p" rel="prev">Dynamic Arrays in C</a>, Up: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="u" rel="up">Multi-dimensional Array Format</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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="Dynamic-Arrays-in-C_002d_002d_002dThe-Wrong-Way"></a>
cannam@167 78 <h4 class="subsection">3.2.5 Dynamic Arrays in C&mdash;The Wrong Way</h4>
cannam@167 79
cannam@167 80 <p>A different method for allocating multi-dimensional arrays in C is
cannam@167 81 often suggested that is incompatible with FFTW: <em>using it will
cannam@167 82 cause FFTW to die a painful death</em>. We discuss the technique here,
cannam@167 83 however, because it is so commonly known and used. This method is to
cannam@167 84 create arrays of pointers of arrays of pointers of &hellip;etcetera.
cannam@167 85 For example, the analogue in this method to the example above is:
cannam@167 86 </p>
cannam@167 87 <div class="example">
cannam@167 88 <pre class="example">int i,j;
cannam@167 89 fftw_complex ***a_bad_array; /* <span class="roman">another way to make a 5x12x27 array</span> */
cannam@167 90
cannam@167 91 a_bad_array = (fftw_complex ***) malloc(5 * sizeof(fftw_complex **));
cannam@167 92 for (i = 0; i &lt; 5; ++i) {
cannam@167 93 a_bad_array[i] =
cannam@167 94 (fftw_complex **) malloc(12 * sizeof(fftw_complex *));
cannam@167 95 for (j = 0; j &lt; 12; ++j)
cannam@167 96 a_bad_array[i][j] =
cannam@167 97 (fftw_complex *) malloc(27 * sizeof(fftw_complex));
cannam@167 98 }
cannam@167 99 </pre></div>
cannam@167 100
cannam@167 101 <p>As you can see, this sort of array is inconvenient to allocate (and
cannam@167 102 deallocate). On the other hand, it has the advantage that the
cannam@167 103 <em>(i,j,k)</em>-th element can be referenced simply by
cannam@167 104 <code>a_bad_array[i][j][k]</code>.
cannam@167 105 </p>
cannam@167 106 <p>If you like this technique and want to maximize convenience in accessing
cannam@167 107 the array, but still want to pass the array to FFTW, you can use a
cannam@167 108 hybrid method. Allocate the array as one contiguous block, but also
cannam@167 109 declare an array of arrays of pointers that point to appropriate places
cannam@167 110 in the block. That sort of trick is beyond the scope of this
cannam@167 111 documentation; for more information on multi-dimensional arrays in C,
cannam@167 112 see the <code>comp.lang.c</code>
cannam@167 113 <a href="http://c-faq.com/aryptr/dynmuldimary.html">FAQ</a>.
cannam@167 114 </p>
cannam@167 115
cannam@167 116
cannam@167 117
cannam@167 118 </body>
cannam@167 119 </html>