如何重现用于拉普拉斯变换的 roc 的侧面带有三角形的垂直条？

Question

这个符号的命令是什么？这个符号表示拉普拉斯变换的ROC界限。查阅了网上的latex文档，还是没找到这个符号。

Answer 1

区分显示和文本样式的版本（不要在下标中尝试）

\documentclass[twocolumn]{article} % twocolumn just for a smaller picture
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\rocl}[3]{%
  % #1 = left bound, #2 = function, #3 = right bound
  \mathopen{}
  \mathpalette\rocl@{{#1}{#2}{#3}}%
  \mathclose{}
}
\newcommand{\rocl@}[2]{\rocl@@{#1}#2}
\newcommand{\rocl@@}[4]{%
  \ifx#1\displaystyle
    {\vphantom{\Big|}}_{#2}\kern-\scriptspace
    \Big|%
    \mspace{-4.5mu}
    \vcenter{\hbox{$\scriptstyle\blacktriangleright$}}%
    \,{#3}\,
    \vcenter{\hbox{$\scriptstyle\blacktriangleleft$}}%
    \mspace{-4.5mu}
    {\Big|}_{#4}%
  \else
    {\vphantom{\big|}}_{#2}\kern-\scriptspace
    \big|%
    \mspace{-4.5mu}
    \vcenter{\hbox{$\scriptscriptstyle\blacktriangleright$}}%
    \,{#3}\,
    \vcenter{\hbox{$\scriptscriptstyle\blacktriangleleft$}}%
    \mspace{-4.5mu}
    {\big|}_{#4}%
  \fi
}
\makeatother

\begin{document}

This $\rocl{\sigma_{\mathrm{L}}}{X(s)}{\sigma_{\mathrm{H}}}$
in text, next in a display
\[
\rocl{\sigma_{\mathrm{L}}}{X(s)}{\sigma_{\mathrm{H}}}
\]
with some text following.

\end{document}

Answer 2

其实，这个公式最难的部分是左边的下标。我发现如果你使用_下面的下标，\vphantom它就不能正常工作，所以我发明了\subdepth{}将下标推到正确的深度。

\documentclass{article}
\usepackage{amssymb}
\newcommand\subdepth[1]{\raisebox{-6pt}{${}_{#1}$}}
\newcommand\midscript[1]{\vcenter{\hbox{$\scriptstyle#1$}}}
\newcommand\ROCl{\Bigl|\mkern-4mu\midscript{\blacktriangleright}}
\newcommand\ROCr{\midscript{\blacktriangleleft}\mkern-4mu\Bigr|}
\begin{document}
$\subdepth{\sigma_L}\ROCl X(s)\ROCr\subdepth{\sigma_H}$
\end{document}

在这里，我将其自动化从 displaystyle 切换到 textstyle，并将调用简化为三参数\ROC宏。

\documentclass{article}
\usepackage{amssymb,amsmath,scalerel}
\makeatletter
\newcommand\subdepth[1]{\ThisStyle{\if D\m@switch
  \raisebox{-6pt}{${}_{#1}$}\else{}_{#1}\fi}}
\newcommand\midscript[1]{\vcenter{\hbox{$\scriptstyle#1$}}}
\newcommand\ROCl{\ThisStyle{\if D\m@switch
  \Bigl|\mkern-4mu\midscript{\blacktriangleright}\else
  |\mkern-4mu\midscript{\blacktriangleright}\fi}}
\newcommand\ROCr{\ThisStyle{\if D\m@switch
  \midscript{\blacktriangleleft}\mkern-4mu\Bigr|\else
  \midscript{\blacktriangleleft}\mkern-4mu|\fi}}
\makeatother
\newcommand\ROC[3]{\subdepth{#1}\ROCl #2\ROCr\subdepth{#3}}
\begin{document}
\[
  \ROC{\sigma_L}{X(s)}{\sigma_H}
\]
\centering
$\ROC{\sigma_L}{X(s)}{\sigma_H}$
\end{document}