Basis set conversion from irreducible spherical tensors into Zeeman basis.
Returns a matrix that converts state vectors written in the spherical tensor basis set used by Spinach into state vectors written in the Zeeman basis set in Liouville space.
P - projector matrix that is to be used in the fol- lowing way: rho_zeeman=P*rho_sphten
The matrix need not be square and may be huge.
Version 2.1, authors: Ilya Kuprov