  Different ways to define and to calculate the degree of spin polarization in
a ferromagnet are discussed, particularly with respect to spin-polarized
tunneling and Andreev reflection at the boundary between a superconductor and
ferromagnet. As an example, the degrees of spin polarization for different
experiments in Fe and Ni are calculated in the framework of the local spin
density approximation (LSDA) and used to illustrate the differences between
various definitions of spin polarization.
