How to elongate down arrow?

Question

\downarrow command is available in directory but it has fixed length. How can I elongate its length?

Answer 1

The \downarrow symbol is an extensible delimiter:

\documentclass{article}

\newcommand{\xdownarrow}[1]{%
  {\left\downarrow\vbox to #1{}\right.\kern-\nulldelimiterspace}
}

\begin{document}

$
\downarrow
\big\downarrow
\Big\downarrow
\bigg\downarrow
\Bigg\downarrow
\xdownarrow{2cm}
$

\end{document}

You can use the same method also for \uparrow, \updownarrow, \Downarrow, \Uparrow and \Updownarrow.

Answer 2

You can define your own command, for example:

The code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}

\newcommand\xdownarrow[1][2ex]{%
   \mathrel{\rotatebox{90}{$\xleftarrow{\rule{#1}{0pt}}$}}
}

\begin{document}

\[
\xdownarrow\quad
\xdownarrow[30pt]\quad
\xdownarrow[2.5cm]
\]

\end{document}

The default length is 2ex and you can control it using the optional argument for \xdownarrow.

With the above definition, the arrow tip will sit on the baseline, you can change the definition to

\newcommand\xdownarrow[1][2ex]{%
   \mathrel{\rotatebox[origin=c]{90}{$\xleftarrow{\rule{#1}{0pt}}$}}
}

for a vertically centered symbol.

Answer 3

You can also draw it with tikz which gives you a lot of flexibility should you desire any customization such as arrow styles, colors, and line styles:

Code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{xparse}% So that we can have two optional parameters

\NewDocumentCommand\DownArrow{O{2.0ex} O{black}}{%
   \mathrel{\tikz[baseline] \draw [<-, line width=0.5pt, #2] (0,0) -- ++(0,#1);}
}

\begin{document}

\[ a
\DownArrow b 
\DownArrow[30pt][>=latex,red, ultra thick] c
\DownArrow[2.5cm][>=stealth,blue, thick, dashed] b
\]

\end{document}

Answer 4

A (similar) alternative, using gathered environment:

\documentclass{article}

\usepackage{amsmath}

\newcommand{\xdownarrow}[2][]{%
\left.{#1}\right\downarrow{#2}}

\begin{document}

$
\xdownarrow[\begin{gathered}
    \vspace{5cm}
    \end{gathered}]{}
$

\end{document}

If you want, it can be used with linebreaks inside:

$
\xdownarrow[\begin{gathered}
    \\
    \\
    \\
    \end{gathered}]{}
$

Usually I use this scheme to place a specific down-arrow across multirows in a table:

\documentclass{article}

\usepackage{amsmath}
\usepackage{multirow}

\newcommand{\xdownarrow}[2][]{%
\left.{#1}\right\downarrow{#2}}

\begin{document}

  \begin{tabular}{cc}
  \hline
  {Lower}   & Text 1\\
  \multirow{2}{*}{$\xdownarrow[\begin{gathered}
  \hfill \\
  \hfill \\
  \hfill \\
  \end{gathered}]{}$ }
            & Text 2\\
            & Text 3\\
            & Text 4\\
            & Text 5\\
  {Higher}  & Text 6\\
  \hline
  \end{tabular}

\end{document}