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Shift theorem : ウィキペディア英語版
Shift theorem

In mathematics, the (exponential) shift theorem is a theorem about polynomial differential operators (''D''-operators) and exponential functions. It permits one to eliminate, in certain cases, the exponential from under the ''D''-operators.
The theorem states that, if ''P''(''D'') is a polynomial ''D''-operator, then, for any sufficiently differentiable function ''y'',
:P(D)(e^y)\equiv e^P(D+a)y.\,
To prove the result, proceed by induction. Note that only the special case

:P(D)=D^n\,
needs to be proved, since the general result then follows by linearity of ''D''-operators.
The result is clearly true for ''n'' = 1 since
:D(e^y)=e^(D+a)y.\,
Now suppose the result true for ''n'' = ''k'', that is,
:D^k(e^y)=e^(D+a)^k y.\,
Then,
:\beginD^(e^y)&\equiv\frac\\\
&\+ae^\\\
&+a\right)(D+a)^ky\right\}\\
&y.\end
This completes the proof.
The shift theorem applied equally well to inverse operators:
:\frac(e^y)=e^\fracy.\,
There is a similar version of the shift theorem for Laplace transforms (t):
:\mathcal(e^ f(t))=\mathcal(f(t-a)).\,


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「Shift theorem」の詳細全文を読む



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