I am using a formula where I have to use $\boldsumbol l$. However on the slide, it looks like the letter capital I. How can I have a nice curvy version to denote vector l?
[Tex/LaTex] Creating curvy symbol for letter ‘l’
symbols
Related Solutions
You have been told how to get a curved L. But here's some more general advice, which also applies in this situation: In cases such as this, always create your own shortcut macro, say
\newcommand{\Lagr}{\mathcal{L}}
This way, if you ever decide that that curly L is not quite the one you like, it is easy to switch. Also, even before you knew the answer to this question, you could have written
\newcommand{\Lagr}{L}
in your preamble. Then you could start/continue writing the document, use ordinary capital Ls where you want, and \Lagr wherever you actually mean a Lagrangian, and then later changing the definition of \Lagr to something appropriate. This way, you wouldn't have to manually search for each occurence of a capital L and decide if it's a Lagrangian or not. Clearly \Lagr (or whatever you want to call this macro) is also easier to type than \mathcal{L}, and it makes the source code much more readable.
Another advantage, which is probably more subtle, since you're new to LaTeX, is that we can make the curvy L exactly the type of math we want. TeX distinguishes between ordinary letters, binary operators, binary relations, opening and closing parenthesis and so on; the spacing between two ordinary letters is not the same as the spacing between the a, +, and b in $a+b$. So since the Lagrangian is a kind of operator, we could say
\newcommand{\Lagr}{\mathop{\mathcal{L}}}
But in the case of operators, the package amsmath (which you are most likely using; if not, you should) provides a somewhat better mechanism:
\DeclareMathOperator{\Lagr}{\mathcal{L}}
Added: Another (related) tip: Even if you are using the same notation for two different things, it is best to make a separate macro for each. In this case you might have
\DeclareMathOperator{\Lagr}{\mathcal{L}}
\DeclareMathOperator{\Lapl}{\mathcal{L}}
The reason is the same as in the L vs. \Lagr case above: If you at some point decide that using \mathcal{L} for both is a bad idea, you would have to find each occurence of \Lagr and figure out if it is really a Laplacian. Using macro names carrying semantic meaning is one of the great powers of TeX.
Use \middle only if there's a \left before it; we can check this using \currentgrouptype (texdoc etex for more information):
\documentclass{article}
\newcommand{\suchthat}{\;\ifnum\currentgrouptype=16 \middle\fi|\;}
\begin{document}
\[
a \suchthat b\qquad\left\{\frac{a}{b}\suchthat x\right\}
\]
\end{document}
Best Answer
Like that?