Agreed. Some of the upsides of eigen compared to lapack relate to the use of expression templates to eliminate temporaries. And the ability to specialize code f

Agreed. Some of the upsides of eigen compared to lapack relate to the use of expression templates to eliminate temporaries. And the ability to specialize code for small fixed size arrays and matrices. If you have large matrices and don’t make use of the expression templates, I would expect performance to be about the same.