Fix bad syntax
[scilab.git] / scilab / modules / fftw / help / en_US / fftw.xml
1 <?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
2 <!DOCTYPE MAN SYSTEM "../../../../modules/helptools/help.dtd">
3 <MAN>
4   <LANGUAGE>eng</LANGUAGE>
5   <TITLE>fftw</TITLE>
6   <TYPE>Scilab Function</TYPE>
7   <DATE>October 2006</DATE>
8   <SHORT_DESCRIPTION name="fftw">fast fourier transform that use fftw library</SHORT_DESCRIPTION>
9   <CALLING_SEQUENCE>
10     <CALLING_SEQUENCE_ITEM>[y]=fftw(x)</CALLING_SEQUENCE_ITEM>
11     <CALLING_SEQUENCE_ITEM>[y]=fftw(x,sign)</CALLING_SEQUENCE_ITEM>
12     <CALLING_SEQUENCE_ITEM>[y]=fftw(x,sign,dim,incr)</CALLING_SEQUENCE_ITEM>
13     <CALLING_SEQUENCE_ITEM>[y]=fftw(x,sign,[dim1 dim2 ...dimN],[incr1 incr2 ...incrN])</CALLING_SEQUENCE_ITEM>
14   </CALLING_SEQUENCE>
15   <PARAM>
16     <PARAM_INDENT>
17       <PARAM_ITEM>
18         <PARAM_NAME>y,x</PARAM_NAME>
19         <PARAM_DESCRIPTION>
20           <SP>: matrix/vector of real/complex data. Input/output data to be transformed.</SP>
21         </PARAM_DESCRIPTION>
22       </PARAM_ITEM>
23       <PARAM_ITEM>
24         <PARAM_NAME>sign</PARAM_NAME>
25         <PARAM_DESCRIPTION>
26           <SP>: Integer. 1 or -1. Set direct or inverse transform.</SP>
27         </PARAM_DESCRIPTION>
28       </PARAM_ITEM>
29       <PARAM_ITEM>
30         <PARAM_NAME>dim</PARAM_NAME>
31         <PARAM_DESCRIPTION>
32           <SP>: integer. Set the dimension (the length) of the transform.</SP>
33         </PARAM_DESCRIPTION>
34       </PARAM_ITEM>
35       <PARAM_ITEM>
36         <PARAM_NAME>incr</PARAM_NAME>
37         <PARAM_DESCRIPTION>
38           <SP>: integer. Set the stride (the span) of the transform.</SP>
39         </PARAM_DESCRIPTION>
40       </PARAM_ITEM>
41     </PARAM_INDENT>
42   </PARAM>
43   <DESCRIPTION>
44     <P>
45     This function realizes direct/inverse Discrete Fourier Transform (DFT) with the help of the FFTW library.
46     </P>
47     <P>
48     One can compute vector, 2D, M-D transform with this function.
49     </P>
50     <P>
51     For more details of fftw syntax see <A href='fft.htm'><VERB>fft</VERB></A> scilab function.
52     </P>
53     <P>
54     For more details about FFTW library see FFTW Web site :<A href='http://www.fftw.org'><VERB> http://www.fftw.org </VERB>.</A>
55     </P>
56     <SP>
57     Remark : fftw function automaticaly stores his last parameters in memory to re-use it in a second time.
58     </SP>
59     <SP>
60     This results on a time computation improvement when consecutives calls (with same parameters) are used.
61     </SP>
62   </DESCRIPTION>
63   <EXAMPLE>
64   <![CDATA[
65   //simple vector direct transform
66   a = rand(50,1)+%i*rand(50,1);
67   y = fftw(a);
68   y = fftw(a,-1);
69   //inverse transform
70   b = fftw(y,1);
71
72   //2D transform
73   a = rand(512,512)+%i*rand(512,512);
74   y = fftw(a);
75
76   //M-D transform -old calling sequence-
77   a = rand(120,1);
78   y = a;
79   dim=[5 6 4];incr=[1 5 30];
80   for i=1:3
81     y = fftw(y,-1,dim(i),incr(i));
82   end
83
84   //M-D transform -new calling sequence-
85   //More efficient than old
86   y = fftw(a,-1,[5 6 4],[1 5 30]);
87   b = fftw(y,1,[5 6 4],[1 5 30]);
88   ]]>
89   </EXAMPLE>
90
91   <SEE_ALSO>
92     <SEE_ALSO_ITEM><LINK>fftw_flags</LINK></SEE_ALSO_ITEM>
93     <SEE_ALSO_ITEM><LINK>get_fftw_wisdom</LINK></SEE_ALSO_ITEM>
94     <SEE_ALSO_ITEM><LINK>set_fftw_wisdom</LINK></SEE_ALSO_ITEM>
95     <SEE_ALSO_ITEM><LINK>fftw_forget_wisdom</LINK></SEE_ALSO_ITEM>
96   </SEE_ALSO>
97
98   <BIBLIO>
99     <P>
100     Matteo Frigo and Steven G. Johnson, &quot;FFTW Manual fo version 3.1.2&quot; June 2006. Available : http://www.fftw.org
101     </P>
102   </BIBLIO>
103
104 </MAN>