I have not used different fonts in a single document before. Therefore, this is a question by an amateur/(or a first-time user).
I want to use AMS Euler font just for a portion of my document. After spending some time on TeX.sx I came up with the following code.
\documentclass[12pt]{report}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{epstopdf}
\usepackage{theorem}
\usepackage{euscript}
\newcommand*{\myfont}{\fontfamily{AMSEuler}\selectfont}
\begin{document}
Using default font: \(\frac{dy}{dx}\)
\begin{myfont}
Using AMSEuler: \(\frac{dy}{dx}\)
\end{myfont}
Back to default font: \(\frac{dy}{dx}\)
\end{document}
The following is the output. It does not look like the AMS Euler font to me. Am I right? If so, how can I select and use AMS Euler font?

NEW EDIT based on comment: I changed the last few lines. However, the output is still the same. The reason is (IMHO) there is no "AMSEuler". Therefore, the question remains. May be, it is not possible to use AMS Euler font this way.
\begin{document}
Using default font: \(\frac{dy}{dx}\)
\myfont{%
Using AMSEuler: \(\frac{dy}{dx}\)
}
Back to default font: \(\frac{dy}{dx}\)
\end{document}


\myfontas a command, but you're using it as an environment. You might want to fix that before anything else. – kahen Oct 08 '11 at 19:27ueur.fd, which is part of the amsfonts collection. i'm not even sure where you got the name "AMSEuler"; it's a reasonable name, but it isn't used anywhere in the ams documentation for these fonts, which is the canonical source, and it also doesn't appear in the comprehensive symbols list. – barbara beeton Oct 08 '11 at 20:05unicode-maththis is rather easy to do: http://tex.stackexchange.com/questions/29498/using-several-math-fonts-with-unicode-math. Problem is that bothunicode-mathand the OpenType Math Euler font (Neo Euler) are still under development, which leads to some annoyances. – Caramdir Oct 08 '11 at 20:30