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

macros

I would like to define a new command (called colim) for filtered colimit (also sometimes called direct limit …) as nice as the command $\varinjlim$ in amsmath package.

So far, I tried $\newcommand{\colim{\operatornamewithlimits{\underset{\longrightarrow{colim}}$

but I find the arrow too thin and its positioning too low compare to $\varinjlim$. How can I get exactly the same (and centered) arrow than this command ?

Edit: with the answer of egreg, it is easy to also get a new command for filtered limit obviously (called colim with a leftarrow below)

Best Answer

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}

Related Solutions

[Tex/LaTex] new command and L with stroke

Focusing on your point that "how can I get an L with a stroke in a different way, so I can still use \L for my boldface L in math mode?", others (notably egreg) have pointed out that it is definitely not a good idea to redefine \L.

But since that was the essence of your question, and if you prefer to throw caution to the wind, you can obtain it thus:

\documentclass[english]{article}
\let\strokeL\L
\renewcommand\L{\mathbf{L}}
\begin{document}
In \strokeL o\'s's Theorem, we need stroke L, but inline, $\L$ gives bold L.
\end{document}

For more ease of use, you could check for the presence of math mode and decide on the fly the definition of \L. That way you could use \L in text and math mode and get your hoped-for result.

\documentclass[english]{article}
\let\strokeL\L
\DeclareRobustCommand{\L}{\ifmmode\mathbf{L}\else\strokeL\fi}
\begin{document}
In \L o\'s's Theorem, we need stroke L, but inline, $\L$ gives bold L.
\end{document}

enter image description here

Thanks to egreg for showing the need for \DeclareRobustCommand in preference to \newcommand, as originally pointed out by David Carlisle. To reiterate, however, experts like egreg caution against the approach of redefining \L.

[Tex/LaTex] New Command For Inline Code

The macro for inputting inline code is \lstinline[option]{<code} Hence use \newcommand{\inlinecode}[1]{\lstinline{#1}}.

\documentclass{article}
\usepackage{listings,lstautogobble}
\usepackage[usenames,dvipsnames]{color}
\newcommand{\inlinecode}[1]{\lstinline{#1}}

% Custom Python Syntax
\lstset
{
    basicstyle=\small\ttfamily,
    commentstyle=\color{Green},
    keywordstyle=\color{Cerulean},
    frame=L,
    language=python,
    morekeywords={True, False},
    numbers=left,
    numbersep=10pt,
    numberstyle=\footnotesize\color{Gray},
    showstringspaces=false,
    stringstyle=\color{Mulberry},
    tabsize=3,
}

% Color Numbers
\lstset
{
    literate=%
    {0}{{{\color{Orange}0}}}1
    {1}{{{\color{Orange}1}}}1
    {2}{{{\color{Orange}2}}}1
    {3}{{{\color{Orange}3}}}1
    {4}{{{\color{Orange}4}}}1
    {5}{{{\color{Orange}5}}}1
    {6}{{{\color{Orange}6}}}1
    {7}{{{\color{Orange}7}}}1
    {8}{{{\color{Orange}8}}}1
    {9}{{{\color{Orange}9}}}1
}

\begin{document}
    To create a new function in Python that took two arguments you would use \inlinecode{def myFunction(x, y):}
\end{document}

enter image description here

But why not use \lstinline directly? Or you can simply do \newcommand{\inlinecode}{\lstinline} as suggested by Werner.

Best Answer

Related Solutions

[Tex/LaTex] new command and L with stroke

[Tex/LaTex] New Command For Inline Code

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