A strange symbol

Question

In the Lathi-Ding's book on communication systems, there is a strange wavy overbar as it is shown in the attached figure ... how can i use it in LaTEX?

Answer 1

You can use the \lfilet growing delimiter of mathabx, sized to the width of the material and rotated.

\documentclass{article}
\usepackage{graphicx}

\DeclareFontFamily{U}{mathx}{}
\DeclareFontSubstitution{U}{mathx}{m}{n}
\DeclareFontShape{U}{mathx}{m}{n}{ <-> s*[0.6]mathx10 }{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareMathDelimiter{\lfilet}{4}{mathx}{"37}{mathx}{"37}

\makeatletter
\DeclareRobustCommand{\overfilet}[1]{{%
  \mathpalette\over@filet{#1}%
}}
\newcommand{\over@filet}[2]{%
  \sbox\z@{$\m@th#1#2\vphantom{^1}$}%
  \sbox\tw@{$\m@th
    #1\left\lfilet\vbox to 0.55\wd\z@{}\right.
    \kern-\nulldelimiterspace
  $}%
  \vbox{\ialign{\hfil##\hfil\cr
    \rotatebox[origin=c]{90}{\box\tw@}\cr
    \noalign{\nointerlineskip}
    \box\z@\cr
  }}%
}
\makeatother

\begin{document}

\[
P_g = \overfilet{g^2(t)} + \overfilet{g(t)g(t\pm\tau)}
\]

\end{document}

With s*[0.4]mathx10 instead of 0.6, the output would be