LaTeX：右侧有两个头的向量

Question

有没有办法使用类似于的东西$\overrightarrow{V}$，即$\twoheadoverrightarrow{\delta}$获得具有两个头的向量？

虽然\twoheadrightarrow已定义，但\twoheadoverrightarrow似乎未定义，那么是否有一些解决方法？

Answer 1

无钛钾Z，只是摆弄amsmath包的内部宏：

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}
\usepackage{amssymb}

\makeatletter

\newcommand*\twoheadrightarrowfill@{%
    \arrowfill@\relbar\relbar\twoheadrightarrow
}
\newcommand*\twoheadleftarrowfill@{%
    \arrowfill@\twoheadleftarrow\relbar\relbar
}
\newcommand*\twoheadoverrightarrow{%
    \mathpalette{\overarrow@\twoheadrightarrowfill@}%
}
\newcommand*\twoheadoverleftarrow{%
    \mathpalette{\overarrow@\twoheadleftarrowfill@}%
}

\makeatother



\begin{document}

In-line: \( \twoheadoverrightarrow{\alpha} + \twoheadoverleftarrow{\beta} \).
Now displayed, with an example of use in subscripts:
\[
    \twoheadoverrightarrow{\alpha} + \twoheadoverleftarrow{\beta}
        + X_{\twoheadoverrightarrow{\delta}}
\]

\end{document}