amsmathbracesspacing
I would like to use an overbrace, but I do not want how much text I put in the overbrace to affect the spacing of the math (i.e. I don't want the the "a" and the "b" to get further apart in the following example):
$\frac{a-\overbrace{b^d}^{\text{'d' here stands for 'dummy variable', it is not an exponent}}}{c}$
Any ideas? This particular example is pretty silly and I would not do it in practice, but it is just to make things simple.
\ldots is using \mathellipsis for the dots. It could be redefined to use the text version, but the mixup of text and math fonts might not always a good idea.
\mathellipsis itself uses three dots as punctuation characters. That means, there is additional thin space between the dots. This can be changed by putting them into a subformula, then they are treated as \mathord atoms without additional space.
\documentclass[12pt]{article}
\usepackage{amsmath}
\renewcommand*{\mathellipsis}{%
\mathinner{{\ldotp}{\ldotp}{\ldotp}}%
}
\begin{document}
$1,2,\ldots,3$
$(1,2,\ldots)$
\end{document}
Usually thin space is the smallest space in math mode, but to some degree \ldots can be adopted to smaller spaces:
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{letltxmacro}
\renewcommand*{\mathellipsis}{%
\mathinner{{\ldotp}{\ldotp}{\ldotp}}%
}
\makeatletter
\@ifdefinable{\org@ldots}{%
\LetLtxMacro\org@ldots\ldots
\DeclareRobustCommand*{\ldots}{%
\ifmmode
\expandafter\my@ldots
\else
\expandafter\textellipsis
\fi
}%
}
\newcommand*{\neghalfmskip}{%
\nonscript\mskip-.5\muexpr\thinmuskip\relax%
}
\newcommand*{\my@ldots}{%
\mathellipsis
\@ifnextchar,\neghalfmskip{%
\@ifnextchar:\neghalfmskip{%
\@ifnextchar;\neghalfmskip{%
\@ifnextchar.\neghalfmskip{%
\@ifnextchar!\neghalfmskip{%
\@ifnextchar?\neghalfmskip{%
\@ifnextchar){\mskip-.5\muexpr\thinmuskip\relax}{% negative kerning
}}}}}}}%
}
\makeatother
\begin{document}
\noindent
$1,2,\ldots,3_{1,2,\ldots,3}$ (ldots)\\
$1,2,\mathellipsis,3_{1,2,\mathellipsis,3}$ (mathellipsis)\\
$(1,2,\ldots)_{(1,2,\ldots)}$ (ldots)\\
$(1,2,\mathellipsis)_{(1,2,\mathellipsis)}$ (mathellipsis)
\end{document}
TeX sets a thin space between inner atoms and punctuation chars in display and text style only, therefore the use of \nonscript. There is no space in case of the closing ), but because of the character shape, you probably want to have a negative kerning, this is applied in all math styles.
The example uses Andrew's hint of \rightdelim@:
\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{letltxmacro}
\renewcommand*{\mathellipsis}{%
\mathinner{{\ldotp}{\ldotp}{\ldotp}}%
}
\makeatletter
\@ifdefinable{\org@ldots}{%
\LetLtxMacro\org@ldots\ldots
\DeclareRobustCommand*{\ldots}{%
\ifmmode
\expandafter\my@ldots
\else
\expandafter\textellipsis
\fi
}%
}
\newcommand*{\neghalfmskip}{%
\nonscript\mskip-.5\muexpr\thinmuskip\relax%
}
\newcommand*{\my@ldots}{%
\mathellipsis
\@ifnextchar,\neghalfmskip{%
\@ifnextchar:\neghalfmskip{%
\@ifnextchar;\neghalfmskip{%
\@ifnextchar.\neghalfmskip{%
\@ifnextchar!\neghalfmskip{%
\@ifnextchar?\neghalfmskip{%
\rightdelim@
\ifgtest@
\mskip-.5\muexpr\thinmuskip\relax% negative kerning
\fi
}}}}}}%
}
\makeatother
\begin{document}
\noindent
$1,2,\ldots,3_{1,2,\ldots,3}$ (ldots)\\
$1,2,\mathellipsis,3_{1,2,\mathellipsis,3}$ (mathellipsis)\\
$(\neghalfmskip\ldots)_{(\neghalfmskip\ldots)}$ (neghalfmskip + ldots)\\
$(\ldots)_{(\ldots)}$ (ldots)\\
$(\mathellipsis)_{(\mathellipsis)}$ (mathellipsis)\\
$\{\ldots\}_{\{\ldots\}}$ (ldots)\\
$\{\mathellipsis\}_{\{\mathellipsis\}}$ (mathellipsis)
\end{document}
But for the detection of an opening delimiter before I do not see a way. There isn't a "\lastmathatom". Manually the space correction can be applied as the example file shows with \neghalfmskip.
It's theoretically possible to make LaTeX recognize clusters of letters and typeset them as if they were input as argument to \mathit, but it would be deadly slow: each alphabetic character should be turned into a “math active” one, which checks whether the following item is an alphabetic character; if it is it should typeset itself, starting \mathit if it's the first one, and then pass the same control to the next character; if not followed by an alphabetic character it should end \mathit.
It's instead better to do something like
\newcommand{\mli}[1]{\mathit{#1}}
where \mli stands for MultiLetter Identifier; use any control sequence name. Then you'd input
$\mli{P}=\mli{NP}$
that has a good deal of advantages, but mainly keeps information about the input.
Note: I have a nice proof of the above statement, but unfortunately there are length limitations for posts on this site.
Heiko's solution in expl3.
\documentclass[fleqn]{article}
\usepackage{xcolor}
\usepackage{amsmath}
\usepackage{xparse}
\ExplSyntaxOn
% 1. Define an equivalent for each letter
\cs_new_protected:Nn \__egreg_letter_loop:nn
{
\int_step_inline:nnn { `#1 } { `#2 }
{
\exp_args:Nc \mathchardef
{ __egreg_letter_code_##1: } % generate the old code
=
\mathcode##1 % the old code
\scan_stop:
\cs_new_protected:cx { __egreg_letter_act_##1: }
{
\exp_not:N \__egreg_letter_scan:nw { ##1 }
}
\char_set_active_eq:nc { ##1 } { __egreg_letter_act_##1: }
}
}
\__egreg_letter_loop:nn { A } { Z }
\__egreg_letter_loop:nn { a } { z }
% 2. Define the main macro that does the scanning
\tl_new:N \l__egreg_letter_scanned_tl
\cs_new_protected:Npn \__egreg_letter_scan:nw #1
{
\tl_if_empty:NT \l__egreg_letter_scanned_tl { \c_group_begin_token } % to be closed later
\tl_put_right:Nx \l__egreg_letter_scanned_tl { \exp_not:c { __egreg_letter_code_#1: } }
\peek_catcode:NF A
{% next char is not a letter
\__egreg_letter_deliver:V \l__egreg_letter_scanned_tl
}
}
\cs_new_protected:Nn \__egreg_letter_deliver:n
{
\tl_if_single:nTF { #1 }
{
\__egreg_letter_single:n { #1 }
}
{
\__egreg_letter_group:n { #1 }
}
\c_group_end_token % finish the group
}
\cs_generate_variant:Nn \__egreg_letter_deliver:n { V }
% 3. The interface for defining the actions
\NewDocumentCommand{\definelettersingle}{m}
{
\cs_set_protected:Nn \__egreg_letter_single:n { { #1 } }
}
\NewDocumentCommand{\definelettergroup}{m}
{
\cs_set_protected:Nn \__egreg_letter_group:n { { #1 } }
}
% 4. Make all letters math active
\int_step_inline:nnn { `A } { `Z } { \mathcode#1="8000 }
\int_step_inline:nnn { `a } { `z } { \mathcode#1="8000 }
\ExplSyntaxOff
% initialize
\definelettersingle{#1}
\definelettergroup{\mathit{#1}}
\begin{document}
First a standard formula $NP\ne N P$
\bigskip
Now \textcolor{blue}{single letters are set in blue},
\textcolor{red}{multiple letters in red}.
\begin{itemize}
\item Multiple letters are put in \verb|\mathit|:
\definelettersingle{{\color{blue}#1}}%
\definelettergroup{\mathit{\color{red}#1}}%
\[ NP \neq N P \]
\item Multiple letters are put in \verb|\mathrm|:
\definelettersingle{{\color{blue}#1}}%
\definelettergroup{\mathrm{\color{red}#1}}%
\[ NP\ (text) \neq N P\ (two\ variables) \]
\[ F_force = m_mass a_acceleration \]
\end{itemize}
\end{document}
Best Answer
Depending on the situation, maybe you can use
\mathclapfrommathtools.For example,