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Multidimensional transform : ウィキペディア英語版
Multidimensional transform
In mathematical analysis and applications, multidimensional transforms are used to analyze the frequency content of signals in a domain of two or more dimensions.

== Multidimensional Fourier transform ==

One of the more popular multidimensional transforms is the Fourier transform, which converts a signal from a time/space domain representation to a frequency domain representation.〔Smith,W. Handbook of Real-Time Fast Fourier Transforms:Algorithms to Product Testing, Wiley_IEEE Press, edition 1, pages 73–80, 1995〕 The discrete-domain multidimensional Fourier transform (FT) can be computed as follows:
: F(w_1,w_2,\dots,w_m) = \sum_^\infty \sum_^\infty \cdots \sum_^\infty f(n_1,n_2,\dots,n_m) e^

where ''F'' stands for the multidimensional Fourier transform, ''m'' stands for multidimensional dimension. Define ''f'' as a multidimensional discrete-domain signal. The inverse multidimensional Fourier transform is given by
: f(n_1,n_2,\dots,n_m) = \left(\frac\right)^m \int_^ \cdots \int_^ F(w_1,w_2,\ldots,w_m) e^ \, dw_1 \cdots \,dw_m
The multidimensional Fourier transform for continuous-domain signals is defined as follows:〔
:F(\Omega_1,\Omega_2,\ldots,\Omega_m) = \int_^ \cdots \int_^
f(t_1,t_2,\ldots,t_m) e^ \, dt_1 \cdots \,dt_m
A fast Fourier transform (FFT) is an algorithm to compute the discrete Fourier transform (DFT) and its inverse. An FFT computes the DFT and produces exactly the same result as evaluating the DFT definition directly; the only difference is that an FFT is much faster. (In the presence of round-off error, many FFT algorithms are also much more accurate than evaluating the DFT definition directly).There are many different FFT algorithms involving a wide range of mathematics, from simple complex-number arithmetic to group theory and number theory. See more in FFT.
The multidimensional discrete Fourier transform (DFT) is a sampled version of the discrete-domain FT by evaluating it at sample frequencies that are uniformly spaced.〔Dudgeon and Mersereau, Multidimensional Digital Signal Processing,2nd edition,1995〕 The DFT is given by:
: Fx(K_1,K_2,\ldots,K_n)= \sum_^ \cdots \sum_^ fx(n_1,n_2,\ldots,n_N) e^ n_1 K_1 -j \frac n_2 K_2 \cdots -j \frac n_m K_m}

for , .
The inverse multidimensional DFT equation is
: fx(n_1,n_2,\ldots,n_m)= \frac \sum_^ \cdots \sum_^ Fx(K_1,K_2, \ldots ,K_m) e^ n_1 K_1 +j \frac n_2 K_2\cdots+j \frac n_m K_m}

for .

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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