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Sampling function : ウィキペディア英語版
Dirac comb

In mathematics, a Dirac comb (also known as an impulse train and sampling function in electrical engineering) is a periodic tempered distribution constructed from Dirac delta functions
:\operatorname_T(t) \ \stackrel\ \sum_^ \delta(t - k T) = \frac\operatorname\left(\frac\right)
for some given period ''T''. The symbol \operatorname(t), where the period is omitted, represents a Dirac comb of unit period. Some authors, notably Bracewell as well as some textbook authors in electrical engineering and circuit theory, refer to it as the Shah function (possibly because its graph resembles the shape of the Cyrillic letter sha Ш). Because the Dirac comb function is periodic, it can be represented as a Fourier series:
:\operatorname_T(t) = \frac\sum_^ e^}.
The Dirac comb function allows one to represent both continuous and discrete phenomena, such as sampling and aliasing, in a single framework of continuous Fourier analysis on Schwartz distributions, without any reference to Fourier series. Owing to the Poisson summation formula, in signal processing, the Dirac comb allows modelling sampling via ''multiplication'' with it, but it also allows modelling periodization via ''convolution'' with it.〔; 1st ed. 1965, 2nd ed. 1978.〕
== Dirac Comb Identity ==

The Dirac comb can be constructed in two ways, either by using the ''comb'' operator (performing sampling) applied to the function that is constantly 1, or, alternatively, by using the ''rep'' operator (performing periodization) applied to the Dirac delta \delta. Formally, this yields
:\operatorname_T \left \ \,=\, \operatorname_T \,=\, \operatorname_T \left \
where
:
\operatorname_T \left \ \,\stackrel\, \sum_^\infty \, f(kT) \, \delta(t-kT)
    and    
\operatorname_T \left \ \,\stackrel\, \sum_^\infty \, g(t-kT)
      ,   .
In signal processing, this property on one hand allows sampling a function f(t) via ''multiplication'' with
\operatorname_T, and on the other hand it also allows the periodization of f(t) via ''convolution''
with \operatorname_T ().

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
ウィキペディアで「Dirac comb」の詳細全文を読む



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