Eigen3: in-place multiplication factor

Both expressions should generate the same code (with a sensibly optimizing compiler), so this is more of a matter of taste.

If you are doing mostly rudimentary operations with a

and b

, you should declare them as Eigen::Array

(instead of Eigen::Matrix

) and just write a*=b;

. If you need access to a

or b

in matrix form later, you can still use a.matrix()

.