How to put bullet symbol on top of downarrow symbol

Question

I want to put bullet symbol on top of downward arrow symbol. Can someone help me on this?

\documentclass{article}
\usepackage{graphicx}

\begin{document}

The transition is represented with $\mathrel{\bullet}\downarrow $ arrow.

\end{document}

Edit1: Actually I want to attach bullet symbol on top of downarrow symbol without any gap.

Answer 1

I don't really know what I'm doing with this, but a suggestion with \ooalign and \mathchoice:

\documentclass{article}
\newcommand\bulletarrow{%
\mathchoice
  {{\ooalign{\raise0.8ex\hbox{$\bullet$}\cr$\downarrow$}}}
  {{\ooalign{\raise0.8ex\hbox{$\bullet$}\cr$\downarrow$}}}
  {{\ooalign{\raise0.65ex\hbox{$\scriptstyle\bullet$}\cr$\scriptstyle\downarrow$}}}
  {{\ooalign{\raise0.5ex\hbox{$\scriptscriptstyle\bullet$}\cr$\scriptscriptstyle\downarrow$}}}%
}

\begin{document}

The transition is represented with $ \bulletarrow_{\bulletarrow_{\bulletarrow}} $ arrow.
\end{document}

For more information about \ooalign see egregs answer to another question.

Answer 2

I just wanted to share this approach. The items are stacked to achieve the desired effect, and the \ThisStyle{...\SavedStyle...} macro of the scalerel package will automatically import the current mathstyle into the macro, into places where the mathstyle would otherwise be lost.

The length \LMpt is a length unit, used inside of the \ThisStyle argument, which is 1pt in \textstyle and \displaystyle, but scales to 0.7pt in \scriptstyle, and 0.5pt in \scriptscriptstyle, so that the relative stacking lengths remain proportional

\documentclass{article}
\usepackage{stackengine}
\usepackage{scalerel}[2014/03/10]
\def\specsym{\ThisStyle{\stackon[-1\LMpt]{$\SavedStyle\downarrow$}{$\SavedStyle\bullet$}}}
\begin{document}
This is the symbol: \specsym, 
$\specsym$ $\scriptstyle\specsym$ $\scriptscriptstyle\specsym$
\end{document}

One could embrace the macro in a \mathord if one desired to use it exclusively in math mode (thanks, egreg).

Thanks also to azetina who, in his answer, makes a good point regarding the use of stackengine. A syntax such as

\stackon[-1\LMpt]{$\SavedStyle\downarrow$}{$\SavedStyle\bullet$}

is easy to visualize and explain. Its drawback is that if you use stacks for other functions in your document, this syntax could be inadvertently affected by the setting of various stackengine defaults, like alignment, etc. One way to avoid this problem is to specify the macro in terms of \stackengine, which is not affected by the changing of package defaults. In the current case, that would mean a more obtuse, but also more protected syntax:

\stackengine{-1\LMpt}{$\SavedStyle\downarrow$}{$\SavedStyle\bullet$}{O}{c}{F}{F}{S}

Answer 3

Using the stackengine package:

\documentclass{article}
\usepackage{amsmath}
\usepackage{stackengine}
\newcommand{\bulletarrow}{%
 \setstackgap{S}{-0.25ex}%
 \mathrel{\Shortstack{{$\bullet$} {$\downarrow$}}}}
\begin{document}
$\bulletarrow$
\end{document}

Another possible definition using the \stackengine command would be:

\stackengine{-0.25ex}{$\downarrow$}{$\bullet$}{O}{c}{F}{T}{S}

Answer 4

You can use \overset from amsmath:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

The transition is represent with $\overset{\bullet}{\downarrow}$ arrow.

\end{document}