Create an S-noise function out of all given parameters.

Input parameters:

1. X0 → X value for function origin.
2. Y0 → Y value for function origin.
3. Fr → Frequency of the primary waveform.
4. Am → Amplitude of maximum combined waveforms.
5. Oc → Number of octaves to include.
6. Dc → Decay factor for each additional octave.
7. An → Angular seed for noise function.

Output parameters:

1. Fn → S-Noise function.