[Tex/LaTex] Underline number in two parts; math mode

bracesmath-mode

I'm trying to underbrace a binary numeral as follow:

  10111101
  '--''---'
    B   D

in order to show the binary-hexadecimal correspondence, but using twice the underbrace command:

\underbrace{1011}_B\underbrace{1101}_D

I get, obviously, two different "words":

  1011 1101
  '--' '---'
    B    D

How can I solve the issue?

Best Answer

\underbrace is defined infontmath.ltx` (part of LaTeX kernel for math stuff) as follows (shortened):

\def\underbrace#1{\mathop{...}\limits}

The construct is defined as math operator (\mathop). This way the lower limit can easily be specified as subscript. But TeX will add a thin space between two \mathop atoms.

This space can be removed by adding a negative thin space \!. Or the whole underbrace construct can be put into curly braces (subformula). Then it becomes an ordinary math atom (\mathord), where TeX will not add spaces inbetween.

The following example shows the differences between the two methods:

\documentclass{article}

\begin{document}
\[
  a
  \underbrace{1011}_B
  \!
  \underbrace{1101}_D
  b
\]
\[
  a
  {\underbrace{1011}_B}
  {\underbrace{1101}_D}
  b
\]
\end{document}

Related Solutions

[Tex/LaTex] Math mode accents and spacing

An accented symbol is treated by TeX as an ordinary one; you have to tell it that you want a relation symbol:

\( w_{1} \mathrel{\tilde{\in}} w_{2} \)

The commands for declaring a math symbol are

\mathord (ordinary)
\mathbin (binary operation)
\mathrel (binary relation)
\mathop (operator, use with care)

An ordinary symbol is typeset without any spacing around it. A binary operation is something like +; for example, if one wanted to define a "mod" operation, a correct way would be

\newcommand{\bmod}{\mathbin{\textrm{mod}}}

(amsmath does it in a quite different way, but that's not the point). A binary relation is like <; the spacing around binary relation symbols is larger than around operation symbols. Moreover the space around relation symbols is uncompressible, while it is for operations.

As already said, putting an accent over a symbol makes it lose its predefined nature: the accented cluster is considered as an ordinary symbol; therefore we have to state explicitly its nature.

[Tex/LaTex] Math mode in longtabu

You need to use $ in the columns with mixed text/math (or alternatively make those math columns and use \text for the text) but the last column is just math so there you can add the $ in the preamble. tabu unfortunately redefines the >{} <{} syntax in an incompatible way but for simple cases, as here, it still works as it should.

All entries in the final column are set in math display style, with no additional markup required for each entry.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tabu}
\usepackage{longtable}
\usepackage{booktabs}
\begin{document}
\tabulinesep=1mm
\begin{longtabu} to \linewidth  {l X[3,c] >{$\displaystyle}X[1,c]<{$}}
  \toprule
  & $f(t)$ & F(s)\\
  \midrule
  1. & Unit impulse $\delta(t)$ & 1\\
  2. & Unit step $1(t)$ &  \frac{1}{s}\\
  3. & $t$ & \frac{1}{s^2}\\
  4. & $\displaystyle \frac{t^n}{(n-1)!} \quad \left(n=1,2,3,\ldots\right)$ & 
                \frac{1}{s^n}\\
  \bottomrule
\end{longtabu}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Math mode accents and spacing

[Tex/LaTex] Math mode in longtabu

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