Currently, mat/scalar or mat/=scalar are optimized as mat*(1/scalar) and mat *= (1/scalar) for non integer scalar types. This might result in invalid result in some borderline cases, as in: http://forum.kde.org/viewtopic.php?f=74&t=107358 Proposal: remove this optimization and leave it to the user.
https://bitbucket.org/eigen/eigen/changeset/93c59c59807e/ changeset: 93c59c59807e user: ggael date: 2012-09-08 11:52:03 summary: fix bug 501: remove aggressive mat/scalar optimization (was replaced by mat*(1/scalar) for non integer types) https://bitbucket.org/eigen/eigen/changeset/11b65f0601c4/ changeset: 11b65f0601c4 branch: 3.1