Why aren't the arrows put under the equal sign if they are less than .7em or .3cm?

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\newcommand{\bigswarrow}[1]{\tikz{\draw[->](#1,3ex)--(0,0);}}
\begin{document}
\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid em}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\bigswarrow{\wid em}}{=}$}

\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\bigswarrow{\wid}}{=}$}
\end{document}

enter image description here

up vote 6 down vote accepted

Adding baseline fixes it, I believe.

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\newcommand{\bigswarrow}[1]{\tikz[baseline]{\draw[->](#1,3ex)--(0,0);}}
\begin{document}
\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid em}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\bigswarrow{\wid em}}{=}$}

\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\bigswarrow{\wid}}{=}$}
\end{document}

enter image description here

Don't know why, but here is a fix. I put the underset arrows inside of an \hbox{...}

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\newcommand{\bigswarrow}[1]{\tikz{\draw[->](#1,3ex)--(0,0);}}
\begin{document}
\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid em}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\hbox{\bigswarrow{\wid em}}}{=}$}

\foreach \wid in {.1,.2,...,1}
{\bigswarrow{\wid}}

\foreach \wid in {.1,.2,...,1}
{$\underset{\hbox{\bigswarrow{\wid}}}{=}$}
\end{document}

enter image description here

Alternately, giving a hat tip to marmot, I could force \bigswarrow onto the baseline by way of stackengine:

\usepackage{stackengine}
\newcommand{\bigswarrow}[1]{\abovebaseline[0pt]{\tikz{\draw[->](#1,3ex)--(0,0);}}}

Then, I wouldn't need the \hboxes.

  • Though the math mode inside the \hbox isn't really necessary, is't it? – campa Nov 9 at 16:58
  • 1
    @campa Thanks. Fixed. – Steven B. Segletes Nov 9 at 17:00

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