{"id":295,"date":"2012-07-02T05:12:15","date_gmt":"2012-07-02T05:12:15","guid":{"rendered":"http:\/\/ahay.org\/blog\/?p=295"},"modified":"2015-09-02T22:56:19","modified_gmt":"2015-09-02T22:56:19","slug":"program-of-the-month-sffft3","status":"publish","type":"post","link":"https:\/\/ahay.org\/blog\/2012\/07\/02\/program-of-the-month-sffft3\/","title":{"rendered":"Program of the month: sffft3"},"content":{"rendered":"

sffft3<\/a> implements a complex-to-complex Fast Fourier Transform (FFT) along an arbitrary axis. <\/p>\n

The FFT library that Madagascar uses by default is KISS FFT<\/a>, created by Mark Borgerding. KISS stands for Keep it simple, Stupid!<\/a> KISS FFT<\/strong> may not be as fast as FFTW<\/a> but it is lightweight and easy to include in the distribution. <\/p>\n

The axis=<\/strong> parameter specifies the data axis for performing the transform. The following example from bei\/ft1\/plane4<\/a> (Jon Claerbout’s Basic Earth Imaging<\/em>) shows different forms of the Fourier transform applied to a 2-D dataset. <\/p>\n

\"\" <\/p>\n

The algorithm in KISS FFT<\/strong> uses a mixed-radix algorithm, which is most efficient when the input size is $N=2^k\\,3^l\\,5^m$. By default, the input data is padded to the next optimal size, additionally multiplied by 2. To disable this behavior, use opt=n pad=1<\/strong>. <\/p>\n

By default, sffft3<\/strong> applies no scaling in the forward transform and $1\/N$ scaling in the inverse transform. To apply a symmetric $1\/\\sqrt{N}$ scaling in both cases, use sym=y<\/strong>. <\/p>\n

For a real-to-complex FFT along the first axis, use sffft1<\/a>. <\/p>\n

For a real-to-real Cosine Fourier Transform, use sfcosft<\/a>. <\/p>\n

To apply FFT as a linear operator, try sffft<\/a> wrapper script. <\/p>\n

10 previous programs of the month:<\/h3>\n