Harmonic Divergence

Harmonic divergence is used to create smooth regular patterns. It's a nice tool for an abstract expressionist. "Kasimir Malevich", "Suprematism", "Evolution of Blue", "Relativism", "Smoky", all these paintings were created just with harmonic.

Harmonic
angle radians or degrees
focus x y
offset horizontal vertical
period horizontal vertical
sub-period horizontal vertical
distortion horizontal vertical
saturation degree of saturation

Remarks
Definition of harmonic function starts with parameters of so-called affine transform. It rotates the pattern around arbitrary "focus" point and shifts it by extent of horizontal and vertical offset. There's common practice to use random numbers in place of affine parameters. It varies a painting but doesn't change its style.
Harmonic pattern has a regular repeating design that reflects the values of period, sub-period and distortion. Each of these parameters is spit on horizontal and vertical parts. Disproportional pairs break the symmetry.
Saturation defines extent of the function peak. If it exceeds the limit an overflow happens. Overflowing visually looks like a number of curved edges with sharp boundaries. The next pictures show common use cases of harmonic function.
period = sub-period
distortion = 0
period = sub-period
distortion = 0.5
period = sub-period
distortion = 2
period < sub-period
distortion = 0
period < sub-period
distortion = 2
period > sub-period
distortion = 0.1
period > sub-period
distortion = 0.6
period > sub-period
distortion = 1.2
period > sub-period
distortion = 1.8
Example
# Creates a randomly rotated 
# harmonic pattern
Harmonic
  angle       random[0:2pi]
  focus       0  0 
  offset      0  0 
  period      2  2
  sub-period  10 10
  distortion  5  5
  saturation  1
...read about Fourier divergence