Economists often denote a Lagrangian maximization problem with a scripted L. Unless you exert a little bit of effort, this looks poorly when produced by LaTeX. The code below allows you to easily typeset the symbol in a larger font-size.
The code creates four new commands: \lagrange1, \lagrange2, \lagrange3, and \lagrange4. They produce the “Lagrangian L” with increasing size.
\documentclass{article}
\usepackage{relsize}
\usepackage{mathrsfs}
\usepackage{xstring}
\newcommand{\lagrange}[1]{\IfEqCase{#1}{{1}{\mathscr{L}}{2}{\mathlarger{\mathscr{L}}}{3}{\mathlarger{\mathlarger{\mathscr{L}}}}{4}{\mathlarger{\mathlarger{\mathlarger{\mathscr{L}}}}}}}
\begin{document}
$$ \lagrange1 $$
$$ \lagrange2 $$
$$ \lagrange3 $$
$$ \lagrange4 $$
\end{document}