double integrals with a bar

Question

I usually use \fint to denote normalized integration. I would like to produce the same slanted line across a double integral \iint. The command \fiint does not seem to exist. How can I get this notation for normalized double integrals?

Answer 1

Using amsmath, esint and graphicx packages, you can declare the \fiint math operator in your preample, as: \DeclareMathOperator*{\fiint}{\ensuremath{\iint\text{\kern-1.36em{\raisebox{5.87pt}{\rotatebox{-93}{$\setminus$}}}}}}.

Answer 2

Borrowing (stealing?!) some code from the posting The Principal Value Integral symbol, here are suggested versions of \dashiint and ddashiint; the former has a single horizontal bar going through the double-integral symbol, and the latter has a double horizontal bar. The following screenshot shows the symbols in display style and text (aka inline-math) style.

\documentclass{article}
\usepackage{amsmath}  % for \iint macro
\usepackage{graphicx} % for \rotatebox and \raisebox macros
\def\Xint#1{\mathchoice
   {\XXint\displaystyle\textstyle{#1}}%
   {\XXint\textstyle\scriptstyle{#1}}%
   {\XXint\scriptstyle\scriptscriptstyle{#1}}%
   {\XXint\scriptscriptstyle\scriptscriptstyle{#1}}%
   \!\iint}
\def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\iint}$}
     \vcenter{\hbox{$#2#3$}}\kern-.51\wd0}}
     
\def\longminus{\raisebox{-2ex}{\rotatebox[origin=c]{20}{${-}\mkern-3.5mu{-}$}}}
\def\longequal{\raisebox{-2ex}{\rotatebox[origin=c]{20}{${=}\mkern-3.5mu{=}$}}}  
\def\dashiint{\Xint\longminus}
\def\ddashiint{\Xint\longequal}

\begin{document}
$\displaystyle\dashiint\ddashiint$
$\dashiint\ddashiint$
\end{document}