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受限乳胶中的化学箭头

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受限乳胶中的化学箭头

我正在编写一些与 LaTeX 渲染器交互的软件。

我需要编写化学反应和平衡，但我无权访问xrightleftharpoons，有没有办法可以在不加载包的情况下内联呈现同样的东西？

我确实可以访问一些包裹的东西：amssymb，，，，，，，。amsmathbmcolor[latin1]inputencflexisymbreqn

答案1

这里我直接从chemarr包，它定义了\xrightleftharpoons您想要的宏。这样，您只需加载amsmath。

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand*{\rightharpoonupfill@}{%
  \arrowfill@\relbar\relbar\rightharpoonup
}

\newcommand*{\leftharpoondownfill@}{%
  \arrowfill@\leftharpoondown\relbar\relbar
}

\newcommand{\xrightleftharpoons}[2][]{%
  \ensuremath{%
    \mathrel{%
      \settoheight{\dimen@}{\raise 2pt\hbox{$\rightharpoonup$}}%
      \setlength{\dimen@}{-\dimen@}%
      \edef\CA@temp{\the\dimen@}%
      \settoheight\dimen@{$\rightleftharpoons$}%
      \addtolength{\dimen@}{\CA@temp}%
      \raisebox{\dimen@}{%
        \rlap{%
          \raisebox{2pt}{%
            $%
            \ext@arrow 0359\rightharpoonupfill@{\hphantom{#1}}{#2}%
            $%
          }%
        }%
        \hbox{%
          $%
          \ext@arrow 3095\leftharpoondownfill@{#1}{\hphantom{#2}}%
          $%
        }%
      }%
    }%
  }%
}
\makeatother

\begin{document}
\[
A \xrightleftharpoons[\mathit{below}]{\mathit{above}} B
\]
\end{document}

在此处输入图片描述

答案2

以下示例使用了\xrightleftharpoons来自包的实现mathtools。它使用了来自包 的宏。该示例还提供了后者的宏，因此不需要amsmath加载。amsmath

\documentclass{article}
%\usepackage{amsmath}% optional

% Implemenation for \xrightleftharpoons taken from package `mathtools'
\makeatletter
\newcommand*\xrightleftharpoons[2][]{%
  \mathrel{%
    \raise.22ex\hbox{%
      $\m@th\ext@arrow 0359\MT@rightharpoonup@fill{\phantom{#1}}{#2}$%
    }%
    \setbox0=\hbox{%
      $\m@th\ext@arrow 3095\MT@leftharpoondown@fill{#1}{\phantom{#2}}$%
    }%
    \kern-\wd0 \lower.22ex\box0 %
  }%
}
\def\MT@rightharpoonup@fill{%
  \arrowfill@\relbar\relbar\rightharpoonup
}
\def\MT@leftharpoondown@fill{%
  \arrowfill@\leftharpoondown\relbar\relbar
}

% The following definitions are taken from package `amsmath'.
\@ifpackageloaded{amsmath}{}{%
  \providecommand*{\arrowfill@}[4]{%
    $\m@th\thickmuskip0mu\medmuskip\thickmuskip\thinmuskip\thickmuskip
     \relax#4#1\mkern-7mu%
     \cleaders\hbox{$#4\mkern-2mu#2\mkern-2mu$}\hfill
     \mkern-7mu#3$%
  }
  \providecommand*{\ext@arrow}[7]{%
    \mathrel{\mathop{%
      \setbox\z@\hbox{#5\displaystyle}%
      \setbox\tw@\vbox{\m@th
        \hbox{$\scriptstyle\mkern#3mu{#6}\mkern#4mu$}%
        \hbox{$\scriptstyle\mkern#3mu{#7}\mkern#4mu$}%
        \copy\z@
      }%
      \hbox to\wd\tw@{\unhbox\z@}}%
    \limits
      \@ifnotempty{#7}{^{\if0#1\else\mkern#1mu\fi
                         #7\if0#2\else\mkern#2mu\fi}}%
      \@ifnotempty{#6}{_{\if0#1\else\mkern#1mu\fi
                         #6\if0#2\else\mkern#2mu\fi}}}%
  }
  \providecommand{\@ifnotempty}[1]{%
    \@ifempty{#1}{}%
  }
  \providecommand{\@ifempty}[1]{\@xifempty#1@@..\@nil}
  \@ifundefined{@xifempty}{%
    \long\def\@xifempty#1#2@#3#4#5\@nil{%
      \ifx#3#4\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi
    }
  }{}
}
\makeatother

\begin{document}
  \[ a \xrightleftharpoons[below]{above} b \]
\end{document}

结果

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