Curve Integral typeset problem

Question

I would like typeset equation on the figure below:

I've tried code:

\begin{equation}\label{fyz:eq_fey_curveint1}
  \Psi(2)-\Psi(1) = 
    \begin{array}{l}
      \displaystyle\int_{(1)}^{(2)}(\nabla\Psi)\cdot\,d{\vec{s}} \\
      \text{po}\,\Gamma
    \end{array}
\end{equation} 

with result:

As you can see on the left hand side of the equation is not correctly centered on the character of the integral. I try use solution from similar problem, discussed at the stackexchange web, but I did not get a satisfactory result. I hope that this group of very experienced users advise me again.

Answer 1

\documentclass[preview,border=12pt]{standalone}
\usepackage{mathtools}
\DeclareMathOperator{\po}{po}

\begin{document}
\abovedisplayskip=0pt\relax% don't use this line in your production
\[
\Psi(2)-\Psi(1) = \int_{\substack{(1)\\\po\Gamma}}^{(2)}(\nabla\Psi)\cdot \textrm{d}\vec{s}
\]
\end{document}

Output

Compare with the scanned image on the question.

Is there any significant difference? I don't think so.

Answer 2

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\Psi(2)-\Psi(1)={\displaystyle
\int_{\underset{\operatorname{{po}\,
\Gamma}}{(1)}}^{(2)}}
(\nabla\Psi)\cdot \mathrm{d}{\vec{s}}
\end{equation}
\end{document}

Answer 3

TeX Primitives are still cool:

\documentclass{article}

\begin{document}
  \begin{equation}\label{fyz:eq_fey_curveint1}
    \Psi(2)-\Psi(1) = 
      \displaystyle\int_{(1)\atop\text{po}\,\Gamma}^{(2)}(\nabla\Psi)\cdot\,\mathrm{d}\vec{s}
  \end{equation}
\end{document}

Edit 1: There is one thing that I would adjust. Instead of the \text{po}\,\Gamma, I would rather do

\usepackage{amsmath}
\DeclareMathOperator{\po}{po}

and replace it by \po\Gamma.

Edit 2: For size correction of the subscript you have to do _{\scriptstyle (1)\atop\scriptstyle\po\Gamma}.

Answer 4

With a new definition of subarray taking also an optional argument [t] (for “top alignment”), the result seems better. The following document shows two variants: one with left alignment in the subarray, the other one with center alignment (and \hidewidth so that the bottom line is “invisible” as far as the width of the subarray is concerned).

\documentclass{article}
\usepackage{amsmath}
\usepackage{bm} % for the bold italic s

\DeclareMathOperator{\po}{po}
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\makeatletter
\renewenvironment{subarray}[2][c]{%
  \if#1t\vtop\else\vcenter\fi\bgroup
  \Let@ \restore@math@cr \default@tag
  \baselineskip\fontdimen10 \scriptfont\tw@
  \advance\baselineskip\fontdimen12 \scriptfont\tw@
  \lineskip\thr@@\fontdimen8 \scriptfont\thr@@
  \lineskiplimit\lineskip
  \ialign\bgroup\ifx c#2\hfil\fi
    $\m@th\scriptstyle##$\hfil\crcr
}{%
  \crcr\egroup\egroup
}
\makeatother

\begin{document}
\[
\psi(2)-\psi(1)=
\int_{\begin{subarray}[t]{l}
      (1)\\
      \po\Gamma
      \end{subarray}}
    ^{(2)}
  (\nabla\psi)\cdot\diff\bm{s}.
\]

\[
\psi(2)-\psi(1)=
\int_{\begin{subarray}[t]{c}
      (1)\\
      \hidewidth\po\Gamma\hidewidth
      \end{subarray}}
    ^{(2)}
  (\nabla\psi)\cdot\diff\bm{s}.
\]

\end{document}

It's not clear whether the psi in the text is lower or upper case; my impression is that it's lower case. The slanted or upright Gamma is probably a stylistic decision.

With the new form of subarray the optional argument can be t or c (which is the default). I don't think adding a b option is worthwhile.