  We present an accurate and efficient method to calculate the effect of random
fluctuations of the local field at the muon, for instance in the case muon
diffusion, within the framework of the strong collision approximation. The
method is based on a reformulation of the Markovian process over a discretized
time base, leading to a summation equation for the muon polarization function
which is solved by discrete Fourier transform. The latter is formally
analogous, though not identical, to the integral equation of the original
continuous-time model, solved by Laplace transform. With real-case parameter
values, the solution of the discrete-time strong collision model is found to
approximate the continuous-time solution with excellent accuracy even with a
coarse-grained time sampling. Its calculation by the fast Fourier transform
algorithm is very efficient and suitable for real time fitting of experimental
data even on a slow computer.
