[Tex/LaTex] Putting \hat over first character of subscripted variable

macrosmath-modesubscripts

I'm using a set of commands to define abstractions of mathematical notations that often occur during my thesis such as:

\newcommand{\DNoise}{n_d}

which would equal some distortion noise. This allows me to quickly change the notation throughout the document with just a change in one place and has proven invaluable so far. Now there is another command

\newcommand{\Est}[1]{\hat{#1}}

which is supposed to put a hat over another symbol to denote it's estimated. Using this with single symbols is all fine but when using it with symbols that have a subscript, the following happens:

Problem

The left one is obtained by \Est{\DNoise} and the right one by \Est{n}_d which is possible but requires to break the pattern used throughout the document. The question is if there is a way to redefine \Est so that it produces the left result even when passed a variable with subscript.

Best Answer

A way to go is

\documentclass{article}

\usepackage{amsmath}

\newcommand{\DNoise}{n_d}

\newcommand{\Est}[1]{\hat{#1}}
\newcommand{\Test}[1]{\expandafter\hat#1}    

\begin{document}

$ \DNoise, \Est{\DNoise}, \Test{\DNoise}$
\end{document}

This produces this output

Output

Related Solutions

[Tex/LaTex] Centered hat over bold letter with subscript in \newcommand

The key was to set your redefinition of \vec in its own group (as denoted with the extra set of braces).

\documentclass{article}
\usepackage{bm}
\renewcommand{\vec}[1]{{\boldsymbol{#1}}}
\newcommand{\gyrobias}{\vec{b}_{g}}
\newcommand{\est}[1]{\hat#1}
\begin{document}
$\est{\gyrobias}$
\end{document}

If this approach does bad things to \vec in some other way, one could always apply the extra group to the definition of \gyrobias, instead:

\documentclass{article}
\usepackage{bm}
\renewcommand{\vec}[1]{\boldsymbol{#1}}
\newcommand{\gyrobias}{{\vec{b}}_{g}}
\newcommand{\est}[1]{\hat#1}
\begin{document}
$\est{\gyrobias}$
\end{document}

FOLLOW UP

With this follow up, I address the issue of getting a \hat or \dot over the intended letter, using the syntax of the OP. However, it does not address the issue of multiple diacritics over the same letter, as in \dot{\est{\camrot}}.

\documentclass{article}
\usepackage{bm}
\renewcommand{\vec}[1]{\boldsymbol{#1}}
\newcommand{\gyrobias}{{\vec{b}}_{g}}
\newcommand{\rquat}[2]{{\overline{q}}^{#1}_{#2}}
\newcommand{\camrot}{\rquat{O}{C}}
\newcommand{\pos}[5][]{{_{#5}}#1{\vec{#2}}_{#3 #4}}
\newcommand{\trans}[4][]{\pos[#1]{t}{#2}{#3}{#4}} %\trans{from}{to}{in}
\newcommand{\campos}[1][]{\trans[#1]{O}{C}{O}}
\newcommand{\est}[1]{\applydiacritic{\hat}{#1}}
\newcommand{\Dot}[1]{\applydiacritic{\dot}{#1}}
\newcommand\applydiacritic[2]{\ifx\campos#2\campos[#1]\else\expandafter#1#2\fi}
\begin{document}
$\est{\gyrobias}$\medskip

$\camrot\quad\est{\camrot}\quad\Dot{\camrot}$\medskip

$\campos\quad\est{\campos}\quad\Dot{\campos}$\medskip
\end{document}

The OP points out that the above code does not work with amsmath. Here is a fix for that, though I note that amsmath package affects the placement of diacritical marks over the letter "t", and I have verified that it is not related to my solution here, which can be seen in the first line of my output (when amsmath is inserted/removed).

\documentclass{article}
\usepackage{bm}
\usepackage{amsmath}% THIS PACKAGE EFFECTS PLACEMENT OF DIACRITICS OVER \boldsymbol{t}
\renewcommand{\vec}[1]{\boldsymbol{#1}}
\newcommand{\gyrobias}[1][]{#1{\vec{b}}_{g}}
\newcommand{\rquat}[3][]{#1{\overline{q}}^{#2}_{#3}}
\newcommand{\camrot}[1][]{\rquat[#1]{O}{C}}
\newcommand{\pos}[5][]{{_{#5}}#1{\vec{#2}}_{#3 #4}}
\newcommand{\trans}[4][]{\pos[#1]{t}{#2}{#3}{#4}} %\trans{from}{to}{in}
\newcommand{\campos}[1][]{\trans[#1]{O}{C}{O}}
\newcommand{\est}[1]{\applydiacritic{\hat}{#1}}
\newcommand{\mydot}[1]{\applydiacritic{\dot}{#1}}
\newcommand\applydiacritic[2]{%
  \ifx\gyrobias#2\gyrobias[#1]\else
  \ifx\campos#2\campos[#1]\else
  \ifx\camrot#2\camrot[#1]\else
  #1#2\fi\fi\fi}
\begin{document}
$\boldsymbol{t}\quad\hat{\boldsymbol t}\quad\dot{\boldsymbol t}$\medskip

$\gyrobias\quad\est{\gyrobias}\quad\mydot{\gyrobias}$\medskip

$\camrot\quad\est{\camrot}\quad\mydot{\camrot}$\medskip

$\campos\quad\est{\campos}\quad\mydot{\campos}$\medskip
\end{document}

Hat over < symbol

I believe this should be reported as a bug in babel-spanish.

Anyway, since typing \widehat{<} is not really good because it will produce wrong spaces, you can use a workaround: define a command before the special action of babel-spanish enters the scene.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[spanish]{babel}

\newcommand{\lesshat}{\mathrel{\widehat{<}}}

\begin{document}

$a<b\lesshat c$

\end{document}

If you want to type \hat{<} or \widehat{<} in the body of the document, you can't unless you load

\usepackage[spanish,es-noquoting]{babel}

but, as I said at the beginning, this would produce wrong spacing because \hat{<} would be considered an ordinary symbol.

Thanks to Dan for pointing out that in a former version of the answer \string was not needed.

Best Answer

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[Tex/LaTex] Centered hat over bold letter with subscript in \newcommand

Hat over < symbol

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