Fokker-Planck equation time-dependent distribution function

Perhaps the most elegant and exact but therefore the most limited approach to the transport properties is through a general equation such as the Boltzmann or Fokker-Planck equation describing the time-dependent distribution functions of the system. The results of the zeroth-order theories can be conveniently cast in the form of the friction constants of irreversible thermodynamics. 

Taking thermal fluctuations into account, the motion of the particle magnetic moment is described by the orientational distribution function W(e,t) that obeys the Fokker-Planck equation (4.90). For the case considered here, the energy function is time-dependent ... 

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