Polarized: Split beam propagation calculations into a computation and measurement step
As can be seen in, for example, this demonstration, four independent simulations need to be run in order to simulate the four channels in a typical polarized reflectometry experiment. Please note that the spin-flip channels will not be identical if non-perfect polarizer and analyzer are used (see here).
Since polarization is calculated in the density matrix formalism (see theory documents), most of the computation is identical for all channels and polarization is then simulated by two matrix multiplications. Hence the result can be reused and evaluated for arbitrarily many polarization (and analyzer) states, leading to potentially significant speedups. Also, analyzer and polarizer parameters can be fitted very cheaply. This requires that the Q axis is identical for all channels.
This also applies to polarized scattering.
Taken over from Redmine 2462.