This module ("Analytical") is based on the following articles and corresponding MATLAB code:
  [1] D. S. Grebenkov, NMR Survey of Reflected Brownian Motion,
      Rev. Mod.Phys. 79, 1077 (2007)
  [2] D. S. Grebenkov, Pulsed-gradient spin-echo monitoring of restricted 
      diffusion inmultilayered structures,
      J. Magn. Reson. 205, 181-195 (2010).