eulerfontsplain-tex
I want to use the AMS Euler font designed by Zapf in my document. I looked for packages on CTAN (e.g., the euler package), but they are specifically designed for LaTeX.
I took a look at the gkpmac.tex file Knuth wrote from Concrete Mathematics and it is likely to contain the answer I am looking for, but I can't fully understand it and determine what lines to extract to an eumac.tex or euler.tex file (I don't know what the naming convention is in that case).
Just add either \usepackage{euler} or \usepackage{eulervm} to your document's preamble:
\documentclass{article}
\usepackage{euler}
\begin{document}
This is good integration.
\[
\int x \,dx = \frac{x^2}{2}+c
\]
\end{document}
The eulervm package includes many revisions by Zapf to the original Euler fonts. If you use the eulervm package, you will probably want to load it with the options euler-digits and euler-hat-accent, i.e., as
\usepackage[euler-digits,euler-hat-accent]{eulervm}
Incidentally, the use of $$ ... $$ to generate display-math equations is heavily deprecated; it's much better to use \[ and \], as I do in the example above. For much more on this subject, please see the postings Why is \[ ... \] preferable to $$ and What are the differences between $$, \[, align, equation and displaymath?
Addendum: There is no text font that's matched perfectly to AMS Euler. If you provide the directive \usepackage{concrete} in the preamble, you'll get the Concrete Roman text font family. Concrete Roman and AMS Euler were used together (very successfully, I'd say) in the textbook Concrete Mathematics, 1st ed. 1988, 2nd. ed. 1994, by Ronald Graham, Donald Knuth, and Oren Patashnik. However, be forewarned that Concrete Roman is a "raster font" and therefore won't look very good on screen. If the font is generated at 600 dpi, it'll look just fine in print; it's only the on-screen look that will likely disappoint. Other text fonts that are known to work well with AMS Euler are Palatino, Aldus, and Melior; perhaps not coincidentally, all three are creations of Hermann Zapf, the designer of the AMS Euler fonts. To set Palatino as the text font of your document, you could, e.g., issue the command \usepackage{newpxtext}.
Looking at mathptmx.sty, the following should do
\font\tenrm=ptmr7t at 10pt % roman text
\font\sevenrm=ptmr7t at 7pt
\font\fiverm=ptmr7t at 5pt
\font\tenbf=ptmb7t at 10pt % boldface extended
\font\sevenbf=ptmb7t at 7pt
\font\fivebf=ptmb7t at 5pt
\font\tensl=ptmro7t at 10pt % slanted roman
\font\tenit=ptmri7t at 10pt % text italic
% for math family 0 we need a font different from ptmr7t
\font\tenrmop=zptmcm7t at 10pt
\font\sevenrmop=zptmcm7t at 7pt
\font\fivermop=zptmcm7t at 5pt
\textfont0=\tenrmop
\scriptfont0=\sevenrmop
\scriptscriptfont0=\fivermop
\font\teni=zptmcm7m at 10pt % math italic
\font\seveni=zptmcm7m at 7pt
\font\fivei=zptmcm7m at 5pt
\font\tensy=zptmcm7y at 10pt % math symbols
\font\sevensy=zptmcm7y at 7pt
\font\fivesy=zptmcm7y at 5pt
\font\tenex=zptmcm7v at 10pt % math extension
\tenrm % choose default
Best Answer
I found this document, User's Guide to AMSFonts Version 2, https://texdoc.org/serve/amsfndoc.pdf/0, which helped guide the plain TeX implementation. See section 5.1 on pp. 12-13.
In the MWE, I activate the fraktur and roman euler fonts, in both medium and bold. Other euler font families (
eusm,eusb, andeuex) should follow the same approach, with different supported sizes foreuex.