Combine blacktriangle and blacktriangledown

Question

I need to combine \blacktriangle and \blacktriangledown so that I get the following result:

I already tried $\stackrel{\blacktriangle}{\blacktriangledown}$ but then the triangle pointing up is bigger than the one pointing down.

The combined symbols should have the same line height as my text, because I need a list like this (here the triangles are a little bit too big)

XXX
XXX
XXX

Answer 1

The following examples stacks the symbols and scales them to fit the line height:

\documentclass{article}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{calc}

\newcommand*{\textdoubletriangle}{%
  \resizebox{!}{\heightof{X}}{%
    \vbox{%
      \hbox{$\blacktriangle$}%
      \nointerlineskip
      \kern.75ex
      \hbox{$\blacktriangledown$}%
    }%
  }%
}

\begin{document}
\textdoubletriangle XXX
\end{document}

Answer 2

You were actually quite close with the idea

\stackrel{\blacktriangle}{\blacktriangledown}

To overcome the problem of the upper symbol being smaller than the lower one, all one needs to do is to insert \textstyle at the beginning of the first argument of \stackrel. To center the resulting symbol vertically on the math axis, you could place the instructions in a \vcenter{\hbox{$ ... $}} wrapper:

\newcommand\bigblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\textstyle\blacktriangle}{\blacktriangledown}$}}}

Medium and small versions of the same construct could be defined via

\newcommand\mediumblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\blacktriangle}{\scriptstyle\blacktriangledown}$}}}

\newcommand\smallblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\scriptscriptstyle\blacktriangle}{%
                              \scriptscriptstyle\blacktriangledown}$}}}

This is what the three symbols look like:

\documentclass{article}
\usepackage{amssymb}

\newcommand\bigblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\textstyle\blacktriangle}{\blacktriangledown}$}}}

\newcommand\mediumblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\blacktriangle}{\scriptstyle\blacktriangledown}$}}}

\newcommand\smallblacktriangleupdown{%
    \vcenter{\hbox{$\stackrel{\scriptscriptstyle\blacktriangle}{\scriptscriptstyle\blacktriangledown}$}}}

\begin{document}
$\bigblacktriangleupdown$ XXXX

$\mediumblacktriangleupdown$ XXXX

$\smallblacktriangleupdown$ XXXX
\end{document}

If you don't want these symbols centered vertically on the math axis and, instead, want their lower tips to "rest" on the baseline, just leave off the \vcenter{\hbox{$ ... $}} wrappers.

Answer 3

Here is an alternative using the stackengine package.

\documentclass[letterpaper]{article}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{stackengine}
\usepackage{calc}

\newcommand{\updowntriangle}{%
    \resizebox{!}{\heightof{X}}{%
    \stackMath\Shortstack[c]{%
        {\blacktriangle}
        \blacktriangledown}%
    }%
}
\begin{document}
\updowntriangle XXXX
\end{document}