Here are some additions to Jeff Weeks' SnapPea that you may find useful. Comments and problems should go to me, Nathan Dunfield, not Jeff. See also the CompuTop.org software list.

## Data and Examples

I have some tables of properties of the SnapPea census manifolds. For the closed manifolds, see also the data associated to my work with Bill Thurston.

I also have SnapPea projections of all knots through 11 crossings and links through 10 crossings. These were computed by Joe Christy, and I have converted them to the modern SnapPea format. Download here. Note added Feb 15, 2006: Prior to this date, the file for the knot 8_19 was incorrect.

## Software

Marc Culler and I wrote and maintain SnapPy, a user interface to the SnapPea kernel which runs on Mac OS X, Linux, and Windows. SnapPy combines a link editor and 3D-graphics for Dirichlet domains and cusp neighborhoods with a powerful command-line interface based on the Python programming language.

SnapPy supersedes the earlier SnapPeaPython written by Jeff Weeks (with improvements by Marc and I) in the 2000s, and the even earlier interface python_snappea which I wrote in grad school. Both of these earlier version are deprecated, and SnapPy is much better and more complete than either of them.

Code from computing the Alexander polynomial of a SnapPy manifold from within Sage. Instructions are at the top of the file. alexander.py

I also have some stand-alone Python programs for generating link projections:

• Note for Mac OS 9 users: If you have trouble, make sure that Netscape et. al isn't mangling the file during download (e.g. by failing to convert the end of line characters). You may need to open the file in Netscape and then copy to SimpleText.
• For creating projections of Montesinos knots: montesinos_projection.py.
• For creating projections of links associated to braids: braids.py.
• For creating projections of knots and links in bridge position: bridge.py.

You will need a Python interpreter (version 1.5 or newer) to run these programs. These are free and available for virtually every platform from the Python home page. If you're using UNIX, you can see if your system has python installed by typing which python (Linux and Mac OS X systems almost always have Python installed).

I also have a variety of C code that extends SnapPea. For these you will need to be able to compile your own version of the SnapPea kernel (experts only ;-). Since I anticipate low demand for these items, send me mail if you want any of them.

• Code for producing a KLProjection of a given braid (in C -- you only want this if the above python program is too slow for your needs).
• Code for producing the Wirtinger presentation for the fundamental group of a link complement from a KLProjection.
• Code for computing homology of manifolds with 100's of tetrahedra w/o overflow (Uses NTL library).
• Code for finding representations of the fundamental group of a manifold into PSL(2, Z_p). Superseded by this Virtual Haken Software.