I'm currently trying to write over/under an implies arrow in LaTeX (in math mode):
\implies_{text}
This places the text lower, but next to the arrow, not below it. How can I get it below the arrow?
[Tex/LaTex] Text over/under implies arrow
amsmathmath-modesymbols
Related Solutions
The problem is this: \Longrigtharrow (over which \implies is defined) is built with two characters that come from different fonts.
The equals sign for lengthening the arrow is taken from \textfont0 (the normal text font), while the arrow (\Rightarrow) is taken from \textfont2 (the math symbol font).
When a current font size is 10pt, lmodern defines \textfont0 as rm-lmr10 (the prefix rm means OT1 encoding) and \textfont2 as lmsy10 and all is good. If the current font size is 11pt, the fonts are rm-lmr10 at 10.95pt and lmsy10 at 10.95pt, which again agree with each other.
The problem is at 12pt: in this case \textfont0 is rm-lmr12, while \textfont2 is lmsy10 at 12pt. Here is where the problem arises: the thickness of the strokes is scaled for \Rightarrow but not with = and the difference is noticeable, particularly at low resolution.
The following image is taken at 4x magnification (\mag=4000) by compiling with pdftex the input
\mag=4000
\font\xy=lmsy10 at 12pt
\font\xz=rm-lmr12
\textfont2=\xy \textfont0=\xz
$\Longrightarrow$
\bye
and the difference cannot be attributed to pixel adjustments of the onscreen previewer.
A possible workaround is to redefine the font used for \textfont0 to use scaled rm-lmr10 when the current font size is above 10pt and using T1 as the default encoding for text fonts.
\documentclass[12pt]{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\makeatletter
% Load the OT1 definitions for lmodern
\input{ot1lmr.fd}
% Change the definition for \OT1/lmr/m/n/<size>
\DeclareFontShape{OT1}{lmr}{m}{n}%
{<-5.5> rm-lmr5 <5.5-6.5> rm-lmr6
<6.5-7.5> rm-lmr7 <7.5-8.5> rm-lmr8
<8.5-9.5> rm-lmr9 <9.5-> rm-lmr10
}{}
\makeatother
\begin{document}
\noindent
$\Longrightarrow$\\
The text font\\
is \expandafter\texttt\expandafter{\fontname\font}
\end{document}
You can use something like A$\,\to\,$B or A\textrightarrow B (in text mode) from the textcomp package:
\documentclass{article}
\usepackage{textcomp}
\begin{document}
A$\,\to\,$B
A\textrightarrow B
\end{document}
Best Answer
You can use
\xRightarrow[below]{above}from themathtools(orextpfeil) package or\xLongrightarrow[below]{above}fromextarrows. (Have a look at “How to look up a math symbol?” for ideas how you can easily find a particular symbol.)If you want to keep the the same arrow length as implies, you can use
\undersetand\oversetfromamsmath, e.g.\underset{below}{\implies}, or maybe\underset{\mathclap{below}}{\implies}(\mathclapmakes it so that “below” doesn’t introduce extra vertical space if it is longer than the arrow. It is included in the immensely usefulmathtoolspackage).