“…Unfortunately, the resulting Gaussian densities are not capable of representing arbitrary density functions that may appear in estimation problems of arbitrary nonlinear systems. Other density representations include Gaussian mixture densities [7], gridbased approaches [8], simple moments of probability density functions [9], exponential densities [3], fourier series [10], [11], the representation by means of sample sets [12], or Dirac mixture densities [13], which are capable of representing more general densities.…”