UnivariateSpectralDensity.m must be implemented to preprocessor and documented.
The SpectralDensity option of stoch_simul is neither documented nor implemented in the preprocessor. It could be implemented as an option of stoch_simul().
Alternatively, we could use a preprocessor command along the lines
which translates into
options_.SpectralDensity.trigger = 1; options_.SpectralDensity.plot = integer; options_.SpectralDensity.cutoff = number; options_.SpectralDensity.sdl = number;