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1 <html lang="en">
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2 <head>
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3 <title>Column-major Format - FFTW 3.3.3</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.3">
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6 <meta name="generator" content="makeinfo 4.13">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format">
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9 <link rel="prev" href="Row_002dmajor-Format.html#Row_002dmajor-Format" title="Row-major Format">
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10 <link rel="next" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C" title="Fixed-size Arrays in C">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.3, 25 November 2012).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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34 <meta http-equiv="Content-Style-Type" content="text/css">
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35 <style type="text/css"><!--
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="Column-major-Format"></a>
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50 <a name="Column_002dmajor-Format"></a>
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51 <p>
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52 Next: <a rel="next" accesskey="n" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C">Fixed-size Arrays in C</a>,
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53 Previous: <a rel="previous" accesskey="p" href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>,
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54 Up: <a rel="up" accesskey="u" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>
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55 <hr>
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56 </div>
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57
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58 <h4 class="subsection">3.2.2 Column-major Format</h4>
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59
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60 <p><a name="index-column_002dmajor-118"></a>
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61 Readers from the Fortran world are used to arrays stored in
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62 <dfn>column-major</dfn> order (sometimes called “Fortran order”). This is
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63 essentially the exact opposite of row-major order in that, here, the
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64 <em>first</em> dimension's index varies most quickly.
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65
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66 <p>If you have an array stored in column-major order and wish to
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67 transform it using FFTW, it is quite easy to do. When creating the
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68 plan, simply pass the dimensions of the array to the planner in
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69 <em>reverse order</em>. For example, if your array is a rank three
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70 <code>N x M x L</code> matrix in column-major order, you should pass the
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71 dimensions of the array as if it were an <code>L x M x N</code> matrix
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72 (which it is, from the perspective of FFTW). This is done for you
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73 <em>automatically</em> by the FFTW legacy-Fortran interface
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74 (see <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a>), but you must do it
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75 manually with the modern Fortran interface (see <a href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>).
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76 <a name="index-Fortran-interface-119"></a>
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77 <!-- =========> -->
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78
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79 </body></html>
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80
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