Often, the tensor of diffusion of cosmic rays in the inner heliosphere is given in terms of $k_{\parallel}$ and $k_\perp$, the coefficients of diffusion along and perpendicular to the magnetic field. These are related to the radial coefficient of diffusion by the relation:
$$k_{rr}= \cos^2\psi k_{\parallel}+\sin^2\psi k_\perp$$ where $\psi$ is the angle between the radial direction and the direction of the magnetic field.
But how are the other components of the tensor of diffusion ($k_{\theta\theta}, \dots$) related to $k_{\parallel}$ and $k_\perp$?
