Hi John,
thanks for using Boost!
Boost.uBlas is a C++ template class library that primarily focuses on BLAS level 1, 2, 3 functionality for dense, packed and sparse matrices, see
https://www.boost.org/doc/libs/1_74_0/libs/numeric/ublas/doc/overview.html#functionality Recently, we also have introduced tensors.
Boost.uBlas is convient in terms familiarity and convenience if you have already experience with Boost and its setup. You will have most basic matrix operations such as matrix-matrix-multiplications. However, more complex linear algebra routines are not yet included.
Eigen is a framework itself and provides you with more functionality for now.
Good luck with your software project.
Best,
CB