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2 <head>
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3 <title>New-array Execute Functions - FFTW 3.2.1</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.2.1">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="FFTW-Reference.html#FFTW-Reference" title="FFTW Reference">
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9 <link rel="prev" href="Guru-Interface.html#Guru-Interface" title="Guru Interface">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.2.1, 5 February 2009).
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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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35 <style type="text/css"><!--
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44 span.sansserif { font-family:sans-serif; font-weight:normal; }
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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 <p>
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50 <a name="New-array-Execute-Functions"></a>
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51 <a name="New_002darray-Execute-Functions"></a>
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52 Next: <a rel="next" accesskey="n" href="Wisdom.html#Wisdom">Wisdom</a>,
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53 Previous: <a rel="previous" accesskey="p" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>,
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54 Up: <a rel="up" accesskey="u" href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>
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55 <hr>
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56 </div>
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57
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58 <h3 class="section">4.6 New-array Execute Functions</h3>
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59
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60 <p><a name="index-execute-256"></a><a name="index-new_002darray-execution-257"></a>
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61 Normally, one executes a plan for the arrays with which the plan was
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62 created, by calling <code>fftw_execute(plan)</code> as described in <a href="Using-Plans.html#Using-Plans">Using Plans</a>.
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63 <a name="index-fftw_005fexecute-258"></a>However, it is possible for sophisticated users to apply a given plan
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64 to a <em>different</em> array using the “new-array execute” functions
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65 detailed below, provided that the following conditions are met:
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66
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67 <ul>
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68 <li>The array size, strides, etcetera are the same (since those are set by
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69 the plan).
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70
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71 <li>The input and output arrays are the same (in-place) or different
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72 (out-of-place) if the plan was originally created to be in-place or
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73 out-of-place, respectively.
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74
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75 <li>For split arrays, the separations between the real and imaginary
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76 parts, <code>ii-ri</code> and <code>io-ro</code>, are the same as they were for
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77 the input and output arrays when the plan was created. (This
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78 condition is automatically satisfied for interleaved arrays.)
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79
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80 <li>The <dfn>alignment</dfn> of the new input/output arrays is the same as that
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81 of the input/output arrays when the plan was created, unless the plan
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82 was created with the <code>FFTW_UNALIGNED</code> flag.
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83 <a name="index-FFTW_005fUNALIGNED-259"></a>Here, the alignment is a platform-dependent quantity (for example, it is
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84 the address modulo 16 if SSE SIMD instructions are used, but the address
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85 modulo 4 for non-SIMD single-precision FFTW on the same machine). In
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86 general, only arrays allocated with <code>fftw_malloc</code> are guaranteed to
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87 be equally aligned (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>).
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88
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89 </ul>
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90
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91 <p><a name="index-alignment-260"></a>The alignment issue is especially critical, because if you don't use
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92 <code>fftw_malloc</code> then you may have little control over the alignment
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93 of arrays in memory. For example, neither the C++ <code>new</code> function
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94 nor the Fortran <code>allocate</code> statement provide strong enough
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95 guarantees about data alignment. If you don't use <code>fftw_malloc</code>,
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96 therefore, you probably have to use <code>FFTW_UNALIGNED</code> (which
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97 disables most SIMD support). If possible, it is probably better for
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98 you to simply create multiple plans (creating a new plan is quick once
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99 one exists for a given size), or better yet re-use the same array for
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100 your transforms.
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101
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102 <p>If you are tempted to use the new-array execute interface because you
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103 want to transform a known bunch of arrays of the same size, you should
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104 probably go use the advanced interface instead (see <a href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>)).
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105
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106 <p>The new-array execute functions are:
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107
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108 <pre class="example"> void fftw_execute_dft(
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109 const fftw_plan p,
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110 fftw_complex *in, fftw_complex *out);
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111
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112 void fftw_execute_split_dft(
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113 const fftw_plan p,
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114 double *ri, double *ii, double *ro, double *io);
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115
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116 void fftw_execute_dft_r2c(
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117 const fftw_plan p,
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118 double *in, fftw_complex *out);
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119
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120 void fftw_execute_split_dft_r2c(
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121 const fftw_plan p,
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122 double *in, double *ro, double *io);
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123
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124 void fftw_execute_dft_c2r(
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125 const fftw_plan p,
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126 fftw_complex *in, double *out);
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127
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128 void fftw_execute_split_dft_c2r(
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129 const fftw_plan p,
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130 double *ri, double *ii, double *out);
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131
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132 void fftw_execute_r2r(
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133 const fftw_plan p,
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134 double *in, double *out);
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135 </pre>
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136 <p><a name="index-fftw_005fexecute_005fdft-261"></a><a name="index-fftw_005fexecute_005fsplit_005fdft-262"></a><a name="index-fftw_005fexecute_005fdft_005fr2c-263"></a><a name="index-fftw_005fexecute_005fsplit_005fdft_005fr2c-264"></a><a name="index-fftw_005fexecute_005fdft_005fc2r-265"></a><a name="index-fftw_005fexecute_005fsplit_005fdft_005fc2r-266"></a><a name="index-fftw_005fexecute_005fdft_005fr2r-267"></a>
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137 These execute the <code>plan</code> to compute the corresponding transform on
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138 the input/output arrays specified by the subsequent arguments. The
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139 input/output array arguments have the same meanings as the ones passed
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140 to the guru planner routines in the preceding sections. The <code>plan</code>
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141 is not modified, and these routines can be called as many times as
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142 desired, or intermixed with calls to the ordinary <code>fftw_execute</code>.
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143
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144 <p>The <code>plan</code> <em>must</em> have been created for the transform type
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145 corresponding to the execute function, e.g. it must be a complex-DFT
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146 plan for <code>fftw_execute_dft</code>. Any of the planner routines for that
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147 transform type, from the basic to the guru interface, could have been
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148 used to create the plan, however.
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149
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150 <!-- -->
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151 </body></html>
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152
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