You may wish to spend some time studying Eigen's own documentation on Cwise functions. The E4A UDF library ports most of these (for dense (non-sparse) matrices at least) to AutoIt. As Eigen does not provide decimal control in its three rounding functions, neither does E4A. Tinkering with $EIGEN_DECIMALS is not the solution, as this controls representation, not content. Internally, storage is either at integer, single, or double precision. How many decimals are accurately captured (in the la