Rader's FFT algorithm: Difference between revisions

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The article titled modulo is not mainly about modular arithmetic; fixing the link.
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:<math>b_q = e^{-\frac{2\pi i}{n} g^{-q} }.</math>
 
===Evaluating the Convolutionconvolution===
 
Since ''n''&ndash;1 is composite, this convolution can be performed directly via the [[convolution theorem]] and more conventional FFT algorithms. However, that may not be efficient if ''n''&ndash;1 itself has large prime factors, requiring recursive use of Rader's algorithm. Instead, one can compute a length-(''n''&ndash;1) cyclic convolution exactly by zero-padding it to a length of at least 2(''n''&ndash;1)&ndash;1, say to a [[power of two]], which can then be evaluated in O(''n'' log ''n'') time without the recursive application of Rader's algorithm.