Brief: When selling a SDK, of which one file is heavily modified from Eigen, what is necessary to comply with MPL? Do we need to provide a link on the main software download/license page to download just the one source file with Eigen-based routines? Or do we just need to provide a link somewhere, say, in the license file, for anyone who downloads the software (whether for free or fee) to the source of the Eigen-derived file?

Background: I work for an academic lab that does methods development in computational biology. We're planning to open source our product to the academic community. Commercial users will pay a fee to license just the software (no source), or they can license the complete SDK. We needed a robust, cross-platform, external library independent, replacement for a dense, real, symmetric, eigenvalue/vector decomposition routine for large matrices with a non-infective license. Eigen was the obvious choice to replace our previous implementation, which could not be redistributed in source form.

Detail: Due to workplace policy, it was necessary to adapt various Eigen routines to use internal data structures and algorithms, which differ substantially from Eigen (no expression templates / aliasing; data storage always row-based, sequential, etc.). The majority of the code likewise was rewritten to use our relatively simple matrix/vectors classes, but about most of the comments are still from Eigen and the algorithms themselves are essentially the same. See the actual source file for details. This may be of use to others in similar situations and so we are happy to provide it, but just want to make sure we abide properly by the license requirements.

Thanks,
Jeff Mendenhall
Senior Programmer / Analyst
Meiler Lab @ Vanderbilt University
Nashville, TN

You have to keep the MPL licence for that file and make its source code available to your users/customers. Since it seems this is still a header file, this second requirement is pretty easy.