Diagrams – Creating a Covering Map Arrow

arrowsdiagrams

I am trying to draw an arrow going down similar to these we usually see in topolgy books. For example, when we study covering spaces we usually put the covering space and then an arrow and then the base space.

Any help is appreciated.

Here is a picture:

Best Answer

I support the use of TikZ for diagrams, but if you are looking for something slightly simpler, you could try the amscd package.

@>>> and @VVV make right and down arrows, respectively. You can also use @<<< and @AAA for left or up arrows. The arrow labels go between the first and second characters or between the second and third characters, depending on whether you want them above/left or below/right.

\documentclass{article}
\usepackage{amscd}
\begin{document}

\[
  \begin{CD}
    E @>\tilde{f}>> F\\
    @V\pi_{E}VV @VV\pi_{F}V\\
    M @>>f> N
  \end{CD}
\]

\end{document}

diagram

Basic Solution:

Now sure exactly what problem you had with using \rotatebox, but it seems to work if used as \rotatebox{-90}{$\dashrightarrow$}:

enter image description here

Notes:

Depending on the actual application this might need to be raised vertically, and that can be down with \raisebox:
```
  \newcommand{\dashdownarrow}{\raisebox{2.0ex}{\rotatebox{-90}{$\dashrightarrow$}}}
```

If it is a binary/relational operator than you can enclose the symbol in \mathbin{}/\mathrel{}:

  \newcommand{\dashdownarrow}{\mathbin{\raisebox{2.0ex}{\rotatebox{-90}{$\dashrightarrow$}}}}

Use `\mathchoice` to auto resize:

As per Gonzalo Medina 's suggestion, to be able to use this for different math sizes such as in subscripts, you can use \mathchoice to ensure that the symbol also adjusts in size depending on the surrounding math environment:

enter image description here

Code:

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

\newcommand\dashdownarrowi{\mathchoice%
    {\rotatebox[origin=c]{-90}{$\displaystyle\dashrightarrow$}}%
    {\rotatebox[origin=c]{-90}{$\displaystyle\dashrightarrow$}}%
    {\rotatebox[origin=c]{-90}{$\scriptstyle\dashrightarrow$}}%
    {\rotatebox[origin=c]{-90}{$\scriptscriptstyle\dashrightarrow$}}%
} 

\newcommand{\dashdownarrow}{\mathrel{\dashdownarrowi}} 

\begin{document} 
    $A\dashdownarrow B\quad M_{A\dashdownarrow B}\quad L_{M_{A\dashdownarrow B}}$ 
\end{document}

Use `\text{}` for auto resizing (and change size):

egreg had provided a simpler way to get the same effect and that is by enclosing the symbol in \text{}, allows it to re size appropriately:

enter image description here

Notes:

In this version I added \scalebox so that you can make the symbol smaller -- adjust the scale factor to suit.
If you desire to move it vertically you can use \raisebox{<length>}{}.

Code:

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

\newcommand\ddaaux{\rotatebox[origin=c]{-90}{\scalebox{0.70}{$\dashrightarrow$}}} 
\newcommand\dashdownarrow{\mathrel{\text{\ddaaux}}}

\begin{document} 
    $A\dashdownarrow B\quad M_{A\dashdownarrow B}\quad L_{M_{A\dashdownarrow B}}$ 
\end{document}

[Tex/LaTex] Arrow Definition in PGF/TikZ

The \arrowsize length is only an auxiliary dimen that you can use to calculate a length. It does not actually have anything to do with size of the arrow tip.

The right extend is the length the line will be shorten when the arrow tip is applied. This also does move the origin of the arrow coordinate system (the \pgfpointorigin you use). You need to take the same amount into consideration if you want to draw the arrow.

The line has to be shortened by 1.5 its width.

The left extend (which is actually only needed if you want to combine arrow tips) is then 5pt-1.5\pgflinewidth. I have used basic TeX dimen calculation and the \pgfutil@tempdima dimen to calculate this so that the PGF math parser isn't needed (as indicated and forced by the + in the extend macros).

The \pgftransformshift macro is used to shift the origin back to the tip of the arrow. The quick version of \pgfpoint is used as its arguments do not need to get parsed by PGF math, either.

Instead of another \pgfpathlineto I used \pgfpathclose (this is the low-level equivalent of -- cycle) even though you use filling and the closing is implied.

The backgrounds library and its gridded option is only used so one can easily spot the coordinates (0,0) and (1,0). The second picture is the result of opacity=.5 and shows the line and the arrow tip separately.

Code

\documentclass[tikz,convert=false]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,backgrounds}

\makeatletter
\pgfarrowsdeclare{ipe arrow}{ipe arrow}{%
  \pgfutil@tempdima=5pt\relax
  \advance\pgfutil@tempdima-1.5\pgflinewidth
  \pgfarrowsleftextend{+-\pgfutil@tempdima}%
  \pgfarrowsrightextend{+1.5\pgflinewidth}%
}{%
  \pgftransformshift{\pgfqpoint{1.5\pgflinewidth}{0pt}}%
  \pgfpathmoveto{\pgfpointorigin}%
  \pgfpathlineto{\pgfqpoint{-5pt}{-1.666pt}}%
  \pgfpathlineto{\pgfqpoint{-5pt}{+1.666pt}}%
  \pgfpathclose
  \pgfusepathqfill
}
\makeatother
\begin{document}

Output

enter image description here

Best Answer

Related Solutions

Arrows – How to Create a Dashed Down Arrow in LaTeX

Basic Solution:

Notes:

Use \mathchoice to auto resize:

Code:

Use \text{} for auto resizing (and change size):

Notes:

Code:

[Tex/LaTex] Arrow Definition in PGF/TikZ

Code

Output

Related Question

Use `\mathchoice` to auto resize:

Use `\text{}` for auto resizing (and change size):