https://www.boost.org/doc/libs/develop/doc/html/accumulators.html Last revised: June 10, 2021 at 02:32:49 GMT https://www.boost.org/doc/libs/master/doc/html/accumulators.html Last revised: June 10, 2021 at 15:48:57 GMT I thought it was related to the regression matrix not being updated but that was fixed while documentation is still stale.