How can I write a double closed path integral? I have searched and I have found only single closed loop integral.
[Tex/LaTex] XeLaTeX Double closed path integral?
fontsmath-modesymbols
Related Solutions
If you redefine the largesymbols font, all large operators will be taken from the Euler font. Moreover, the call is wrong:
\DeclareSymbolFont{eulargesymbols}{U}{zeuex}{m}{n}
\DeclareMathSymbol{\intop}{\mathop}{eulargesymbols}{"52}
Here is the picture (on the right the usual symbol)
How does one discover what should be done? Well, it depends on the font one has to use. Let's make an example: we want some large symbols from the font used by mathpazo.
We find in mathpazo.sty what font is used:
\DeclareSymbolFont{largesymbols}{OMX}{zplm}{m}{n}
Thus we just change the symbolic name to something like pazolargesymbols and do as the previous case; since the encoding is OMX, which is the same normally used for math extension fonts, we know that the integral will be in the same slot as in the usual setting:
\DeclareMathSymbol{\intop}{\mathop}{pazolargesymbols}{"52}
One can find the standard definition in fontmath.ltx.
If the encoding is non standard, as in the case of eulervm, we need to check for the slot. However, eulervm.sty doesn't redefine \intop, so we can be confident that the usual slot is good. It could be different for other symbols.
Note that we have to define \intop rather than \int, because the latter is defined by LaTeX as
\def\int{\intop\nolimits}
The amsmath package does a different definition of \int, but it uses \intop for the symbol as well.
A version where the limits are underneath the integral signs:
\documentclass{article}
\usepackage{amsmath,esint}
\newcommand*\VF[1]{\mathbf{#1}}
\newcommand*\dif{\mathop{}\!\mathrm{d}}
\begin{document}
\begin{align*}
\iiint\limits_V (\nabla \cdot \VF{F}) \dif V
&= \oiint\limits_{S(V)} \VF{F} \cdot \hat{\VF{n}} \dif S\\
\iiint\limits_V (\nabla \times \VF{F}) \dif V
&= \oiint \hat{\VF{n}} \times \VF{F} \dif S
\end{align*}
\end{document}
A version where the limits are beside the integral signs:
\documentclass{article}
\usepackage{amsmath,esint}
\newcommand*\VF[1]{\mathbf{#1}}
\newcommand*\dif{\mathop{}\!\mathrm{d}}
\begin{document}
\begin{align*}
\iiint_{V} (\nabla \cdot \VF{F}) \dif V
&= \oiint_{S(V)} \VF{F} \cdot \hat{\VF{n}} \dif S\\
\iiint_{V} (\nabla \times \VF{F}) \dif V
&= \oiint \hat{\VF{n}} \times \VF{F} \dif S
\end{align*}
\end{document}
Note: As pointed out by Charles Staats, the upright d in a differential is not common notation in all branches of science; for an italic d, simply use a d without \mathrm.
Best Answer
The symbol you're looking for is called
\oiint, but you need eitheresintorunicode-mathfor accessing it:If you don't want (or can't) load
unicode-math, then\oiintis available throughesint, as explained in which package for \oiint symbolHow did I find the name? I searched for "integral" with a program that knows all Unicode (I use UnicodeChecker on Mac OS X). Going through the list I found U+222F. Then I looked in
unicode-math-table.tex: from a shell I didand searched for
222Fwhich pointed to the line