# Feyn font

A package of fonts for displaying Feynman diagrams.

Version 0.4.3, 2022 July 20.

- Canonical URL: `https://purl.org/nxg/dist/feyn`
- Repository

This package is intended to produce relatively simple Feynman diagrams, primarily for use within equations.

This package differs from Thorsten Ohl’s `feynmf/feynmp` package (at CTAN, or see the TeX FAQ). FeynMP works by creating Metafont or MetaPost figures using a preprocessor. It’s more general than this package, but is at its best when creating relatively large diagrams, for figures. In contrast, the present system consists of a carefully-designed font with which you can easily write simple diagrams, within equations or within text, in a size matching the surrounding text size.

The propagators and vertices which are implemented are those which seem to appear most often in non-figure displays (the practical definition of ‘appear most often’ is ‘which I wanted’ and ‘which people asked me for’). I have no current plans to extend the package further, but I’m willing add other features if you can make a case for them.

There is further documentation, plus numerous examples, in the package documentation.

[By the way, I have little idea of how many people actually use this package. If you do use it, I’d be most grateful if you could drop me a line just to say so]

## Licence

This software is copyright 1991, 1994, 2001-2, 2005, 2008-17, Norman Gray.. It is distributed under the terms of the 2-clause BSD Licence.

## History

Version 0.4.3, 2022 July 20
  Documentation update, including fixes for broken URIs, and more consistent use of the canonical homepage URI, `https://purl.org/nxg/dist/feyn`.
Version 0.4.2, 2022 July 18

  No code changes, but updates to URLs, including the repository location.

Version 0.4.1, 2017 November 3

  The package is now licensed under the terms of the 2-clause BSD licence.

  The only other changes from v0.4b2 are mild documentation adjustments (sorry for the long delay between 0.4b2 and 0.4).

  Version 0.4 was not widely released.

Version 0.4b3, 2013 April 12
  - Changed `\below` to `\belowl`, and added companion `\belowr`.
  - Documentation updates
Version 0.4b2, 2011 April 9

  As for version 0.4b1, but with the addition of `aV` for a backward arrow (rarely used, but included for consistency; thanks to Thomas Pruschke for the suggestion). Also added: `flo` for the closed fermion loop, for phi^4 theory (plus `floV` and `floA` for completeness; thanks to Hoang Nghia Nguyen for the suggestion; the font should now be able to produce all scalar theory diagrams).

Version 0.4b1, 2010 January 23

  Addition of the extended-size `feynx' fonts, and the `\FEYN` macro (thanks to Luciano Pandola for the suggestion).

  Adjustments to the sizing of half-loops (the half-loops are now squashed, though the quarter-loops aren't). Added ghost loops; we can now do all the diagrams of 2-loop QCD. The quarter-loop gluons now taper at both ends, so that two quarter-loops are no longer the same as one half-loop.

...
  Earlier release notes are available

## Download and installation

The nominal distribution point for the Feyn package is CTAN, under fonts/feyn.

The feyn package is included in the TeXLive distribution, so you may have it on your machine already. If not, or if you need a more up-to-date version, read on.

Since the package is on CTAN, it should be easily installed and updated using the tools which support this in your TeX distribution. For TeXLive, that's tlmgr, and for MikTeX see the maintenance section of the manual.

### Doing the installation by hand

...how thoroughly old-skool of you!

1. Download either feyn-0.4.3.tar.gz or feyn-0.4.3.zip and unpack it.
2. Run LaTeX on the file `feyn.ins` – this will unpack the style file `feyn.sty` amongst other files. Place this ‘somewhere where TeX can find it’. Similarly, place the `.mf` files somewhere where the font-generation mechanism for your platform can find them. For example, in the TeXLive distribution, the feyn `*.mf` files appear in the directory `/usr/local/texlive/2008/texmf-dist/fonts/source/public/feyn/` and the `feyn.sty` file in `/usr/local/texlive/2008/texmf-dist/tex/latex/feyn/feyn.sty`, so that if I were installing them ‘privately’, I would put them in `/usr/local/texlive/texmf-local/fonts/source/local/feyn/` and `/usr/local/texlive/texmf-local/tex/latex/feyn/feyn.sty`. With the teTeX and TeXLive Unix distributions, the output of `kpsepath mf` shows the list of places where TeX will look for Metafont source files. The font files should be generated on the fly when you first refer to them. See also the relevant discussion in the TeX FAQ about ‘where LaTeX can find them’.
3. Run LaTeX on the file `feyn.dtx` to obtain the documentation, which is prebuilt in `feyn.pdf` (this should generate the font files as a side-effect).

You should be able to find generic instructions for installing LaTeX files at the TeX FAQ.

Norman Gray
2022 July 20