Hi list, I have written an open-source (BSD-licensed) algorithm to compare two crystal structure descriptions and identify whether they describe the same underlying structure. The algorithm is capable of detecting degenerate descriptions (meaning unit cell vectors + atomic positions and types) even in the presence of the "real-world" issues confronting computational crystallographers (choice of unit cell representation and offset, rotations, reflections, and numerical noise). The algorithm returns a boolean match using customizable tolerances. I just wanted to inform the mailing list of this, in case such functionality is needed by your user community. The code, XtalComp, is written in C++ and is easy to interface with, having no external dependencies. The liberal license would allow it to be included with the cctbx sources and interfaced with cctbx code if desired. The code uses the CMake build system, but the simple nature of the sources would allow trivial porting to SCons. There is a web interface to the code here: http://xtalopt.openmolecules.net/xtalcomp/xtalcomp.html Also on that page are links to the journal article describing the algorithm, as well as a free download of the preprint version of the article. The code is available on Github (http://www.github.com/dlonie/XtalComp). Thanks for your time, and I hope that someone out there will find this code useful :-) Keep up the good work! Dave