Creating a new command for physical versors

amsmathmacros

I am trying to create a command in order to achieve this:

I would like to write:

\ver{x} , \ver{y} , \ver{z} , \ver{r} , etc…

And I would like to get:

\hat{\mathbf{x}} , \hat{\mathbf{y}} , \hat{\mathbf{z}} , \hat{\mathbf{r}} … respectively.

I need a command capable of doing this for every letter I put between {}.

I have tried \newcommand{\ver}{\hat\mathbf} but I am getting error: extra or forgotten }.

I have also tried \newcommand{\ver}{\hat{\mathbf{•}}} or \newcommand{\ver{•}{\hat{\mathbf{•}}} but I get no result.

If anyone knows how can I solve this problem I will appreciate it.

Best Answer

You might do

\newcommand{\ver}[1]{\hat{\mathbf{#1}}}

but the result of \ver{i} would not be nice, because the i should lose the dot.

\documentclass{article}
\usepackage{amsmath}

\DeclareSymbolFont{mathbf}{OT1}{\familydefault}{\bfdefault}{n}
\DeclareSymbolFontAlphabet{\mathbf}{mathbf}
\DeclareMathSymbol{\boldimath}{\mathord}{mathbf}{"10}
\DeclareMathSymbol{\boldjmath}{\mathord}{mathbf}{"11}

\newcommand{\ver}[1]{% we assume #1 is a single Latin letter
  \if#1i%
    \hat{\boldimath}%
  \else
    \if#1j%
      \hat{\boldjmath}%
    \else
      \hat{\mathbf{#1}}%
    \fi
  \fi
}

\begin{document}

$\ver{a}+\ver{c}+\ver{i}+\ver{j}+\ver{k}+\ver{x}$

\end{document}

A version that also works with Greek letters.

\documentclass{article}
\usepackage{amsmath,bm}

% for the dotless i and j in bold face upright
\DeclareSymbolFont{mathbf}{OT1}{\familydefault}{\bfdefault}{n}
\DeclareSymbolFontAlphabet{\mathbf}{mathbf}
\DeclareMathSymbol{\boldimath}{\mathord}{mathbf}{"10}
\DeclareMathSymbol{\boldjmath}{\mathord}{mathbf}{"11}

\ExplSyntaxOn

\NewDocumentCommand{\ver}{m}
 {% Assumption: the argument is
  % either a single Latin letter or
  % or a single command for a Greek letter
  \token_if_cs:NTF #1
   { \hat{\bm{#1}} } % single Greek letter
   {% check for i or j
    \str_case:nnF { #1 }
     {
      {i}{\hat{\boldimath}} 
      {j}{\hat{\boldjmath}}
     }
     { \hat{\mathbf{#1}} } % single Latin letter not i nor j
   }
 }

\ExplSyntaxOff

\begin{document}

$\ver{a}+\ver{c}+\ver{i}+\ver{j}+\ver{k}+\ver{x}+\ver{\alpha}+\ver{\Gamma}$

\end{document}

Remember to add \usepackage{xparse} if this seems not to work (and update your TeX system).

Related Solutions

[Tex/LaTex] Bold or arrow vectors with new command

Do you want this?

possible target

\documentclass[a4paper,11pt]{report}
\DeclareMathAlphabet      {\mathbfit}{OML}{cmm}{b}{it}
\usepackage[T1]{fontenc}
\usepackage[utf8x]{inputenc}
\usepackage{lmodern}
\usepackage{amsmath}

% \newcommand{\vect}[1]{\vec{#1}}
\newcommand{\vect}[1]{\boldsymbol{\vec{#1}}}

\begin{document}

  \begin{gather}
\rho = \rho _{0}(\vect{x} , t) + \varepsilon \rho _{1}(\vect{x},t) \\
p = p _{0}(\vect{x} , t) + \varepsilon p _{1}(\vect{x},t) \\
\vect{u}=\vect{u} _{0}(\vect{x},t) + \varepsilon\vect{u} _{1}(\vect{x},t)
\end{gather}

\end{document}

Note that when you say

\newcommand\somecommand[2]{something to do}

you are defining a command with two mandatory arguments so you must write

\somecommand{first argument}{second argument}

If you want one argument to be optional, allowing you to write

\somecommand[first argument]{second argument}

\somecommand{second argument only}

you need

\newcommand\somecommand[2][default value for first argument]{something to do}

However, you only seem to be using one argument in your definition which did not try to tell TeX you wanted a vector (no \vec involved) so it did what you asked and just made the argument bold as requested.

Note that this may well fail to answer your question since I am not at all sure I understand it, but it is too much for a comment!

[Tex/LaTex] New command for filtered colimits and limits

Adapt the definition of \varinjlim:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\colim@}[2]{%
  \vtop{\m@th\ialign{##\cr
    \hfil$#1\operator@font colim$\hfil\cr
    \noalign{\nointerlineskip\kern1.5\ex@}#2\cr
    \noalign{\nointerlineskip\kern-\ex@}\cr}}%
}
\newcommand{\colim}{%
  \mathop{\mathpalette\colim@{\rightarrowfill@\textstyle}}\nmlimits@
}
\makeatother

\begin{document}

\[
\colim_{\delta\in\Delta}F_\delta=F
\]

\end{document}

A variant, suggested by Manuel, with a smaller arrow. However, this also requires a redefinition of \varprojlim and \varinjlim for uniformity:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\colim@}[2]{%
  \vtop{\m@th\ialign{##\cr
    \hfil$#1\operator@font colim$\hfil\cr
    \noalign{\nointerlineskip\kern1.5\ex@}#2\cr
    \noalign{\nointerlineskip\kern-\ex@}\cr}}%
}
\newcommand{\colim}{%
  \mathop{\mathpalette\colim@{\rightarrowfill@\scriptscriptstyle}}\nmlimits@
}
\renewcommand{\varprojlim}{%
  \mathop{\mathpalette\varlim@{\leftarrowfill@\scriptscriptstyle}}\nmlimits@
}
\renewcommand{\varinjlim}{%
  \mathop{\mathpalette\varlim@{\rightarrowfill@\scriptscriptstyle}}\nmlimits@
}
\makeatother

\begin{document}

\[
\colim_{\delta\in\Delta}F_\delta
\quad
\varinjlim_{\delta\in\Delta}F_\delta
\quad
\varprojlim_{\delta\in\Delta}F_\delta
\]

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Bold or arrow vectors with new command

[Tex/LaTex] New command for filtered colimits and limits

Related Question