WolframAlpha me dice que $$\int_{-\infty}^{\infty} e^{-(t-i)^4} \, \mathrm{d}t = 0.$$ I am suspicious of this, because of the idea that for nice enough $f $, since $$\int_{-\infty}^{\infty} f(t-a) \, \mathrm{d}t$$ is holomorphic in $ un $ and takes the same value for all $a \in \mathbb{R}$, it should be independent of $a$ by the identity principle; and then $$\int_{-\infty}^{\infty} e^{-(t-i)^4} \, \mathrm{d}t = \int_{-\infty}^{\infty} e^{-t^4} \, \mathrm{d}t = 2 \cdot \Gamma(5/4).$$ But WolframAlpha even tells me numerically that $\int_{-\infty}^{\infty} e ^ {-(t-i) ^ 4} \, \mathrm{d}t$ is close to $0$. ¿Estoy haciendo algo mal?
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Como User8128 comentado, yo creo que son perfectamente correctas.
Sin el cambio de variable y el uso de CAS otro $$\int e^{-(t-i)^4} \, dt=\color{red}{-\frac{(t-i)\, \Gamma \left(\frac{1}{4},(t-i)^4\right)}{4 \sqrt[4]{(t-i)^4}}}=-\frac{1}{4} (t-i) E_{\frac{3}{4}}\left((t-i)^4\right)$$ $$\int_{-\infty}^{\infty} e^{-(t-i)^4} \, dt=i \left(E_{\frac{3}{4}}(-4)-\Re\left(E_{\frac{3}{4}}(-4)\right)\right)$$ $$\int_{-\infty}^{\infty} e^{-(t-i)^4} \, dt=\frac{(-1)^{1/4}\, \Gamma \left(\frac{1}{4},-4\right)}{\sqrt{2}}-i \Re\left(-\frac{(-1)^{3/4}\, \Gamma \left(\frac{1}{4},-4\right)}{\sqrt{2}}\right)=2\, \Gamma \left(\frac{5}{4}\right) $$ Observe que, para el idefinite integral, Wolfram Alpha informa correctamente la expresión escrita en rojo.
Lo que es interesante es que, si le preguntas a Wolfram Alpha $$\int_{0}^{\infty} e^{-(t-i)^4} \, dt=-\frac i4E_{\frac{3}{4}}(-1)$$ $$\int^{0}_{-\infty} e^{-(t-i)^4} \, dt=+\frac i4E_{\frac{3}{4}}(-1)$$ leading to the $0$ usted obtiene.
Es evidente que hay un error que le sugiero que se informe.
Felix Marin
Puntos
32763
$\newcommand{\bbx}[1]{\,\bbox[15px,border:1px groove armada]{\displaystyle{#1}}\,} \newcommand{\llaves}[1]{\left\lbrace\,{#1}\,\right\rbrace} \newcommand{\bracks}[1]{\left\lbrack\,{#1}\,\right\rbrack} \newcommand{\dd}{\mathrm{d}} \newcommand{\ds}[1]{\displaystyle{#1}} \newcommand{\expo}[1]{\,\mathrm{e}^{#1}\,} \newcommand{\ic}{\mathrm{i}} \newcommand{\mc}[1]{\mathcal{#1}} \newcommand{\mrm}[1]{\mathrm{#1}} \newcommand{\pars}[1]{\left(\,{#1}\,\right)} \newcommand{\partiald}[3][]{\frac{\partial^{#1} #2}{\parcial #3^{#1}}} \newcommand{\raíz}[2][]{\,\sqrt[#1]{\,{#2}\,}\,} \newcommand{\totald}[3][]{\frac{\mathrm{d}^{#1} #2}{\mathrm{d} #3^{#1}}} \newcommand{\verts}[1]{\left\vert\,{#1}\,\right\vert}$ \begin{align} \int_{-\infty}^{\infty}\expo{-\pars{t - \ic}^{4}}\dd t & = \int_{0}^{\infty}\bracks{\expo{-\pars{t - \ic}^{4}} + \expo{-\pars{-t - \ic}^{4}}}\dd t = 2\,\Re\int_{0}^{\infty}\expo{-\pars{t + \ic}^{4}}\dd t = 2\,\Re\int_{\ic}^{\infty + \ic}\expo{-t^{4}}\dd t \\[5mm] & = -2\,\lim_{R \to \infty}\Re\int_{1}^{0}\expo{-\pars{R + \ic y}^{4}}\ic\,\dd y - 2\,\Re\int_{\infty}^{0}\expo{-t^{4}}\dd t - 2\,\Re\int_{0}^{1}\expo{-\pars{\ic y}^{4}}\ic\,\dd y \\[5mm] & = -2\,\lim_{R \to \infty}\Im\int_{0}^{1}\expo{-\pars{R + \ic y}^{4}}\,\dd y + {1 \over 2}\int_{0}^{\infty}t^{-3/4}\expo{-t}\,\dd t \\[5mm] & = -2\,\lim_{R \to \infty}\Im\int_{0}^{1}\exp\pars{-R^{4} - 4R^{3}y\ic + 6R^{2}y^{2} + 4Ry^{3}\ic - y^{4}}\,\dd y + {1 \over 2}\,\Gamma\pars{1 \over 4} \\[1cm] & = {1 \over 2}\,\Gamma\pars{1 \over 4} \\[2mm] & - 2\lim_{R \to \infty}\braces{% \expo{-R^{4}}\int_{0}^{1}\exp\pars{y^{2}\bracks{6R^{2} - y^{2}}} \sin\pars{4Ry\bracks{y^{2} - R^{2}}}\,\dd y} \end{align}
- $\ds{y^{2}\pars{6R^{2} - y^{2}}}$ tiene un máximo en $\ds{y_{m} = \root{3}R}$. $\ds{y_{m} > 1}$ al $\ds{R > {\root{3} \over 3}}$.
- Se desvanece en $\ds{y = 0}$ y a las $\ds{y = \root{6}R}$.
- Es $\ds{\to -\infty}$ al $\ds{y \to \infty}$.
- Es claro que $\ds{0 < y^{2}\pars{6R^{2} - y^{2}} < 6R^{2} - 1}$ al$\ds{y \in \pars{0,1}}$$\ds{R > {\root{3} \over 3}}$.
A continuación, \begin{align} 0 & < \verts{\expo{-R^{4}}\int_{0}^{1}\exp\pars{y^{2}\bracks{6R^{2} - y^{2}}} \sin\pars{4Ry\bracks{y^{2} - R^{2}}}\,\dd y}_{\ R\ >\ \!\root{3}/3} \\[5mm] & < \expo{-R^{4}}\int_{0}^{1}\exp\pars{1^{2}\bracks{6R^{2} - 1^{2}}}\,\dd y = \exp\pars{-R^{4} + 6R^{2} - 1} \,\,\,\stackrel{\mrm{as}\ R\ \to\ \infty}{\to}\,\,\, \color{#f00}{\large 0} \end{align}
\begin{align} \mbox{such that}\quad \bbx{\int_{-\infty}^{\infty}\expo{-\pars{t - \ic}^{4}}\dd t = {1 \over 2}\,\Gamma\pars{1 \over 4}} \approx 1.8128 \end{align}
