This is the numerical model for 2-site exchange using 3D magnetisation vectors.
It is selected by setting the model to '''NS R1rho 2-site'''.
The simple constraint $\textrm{pAp_A} > \textrm{pBp_B}$ is used to halve the optimisation space, as both sides of the limit are mirror image spaces.
For this model, the equations from Korzhnev05 have been used.