A complex curved or wave-like line can consist of:

1. geometric part of a circle, or
2. free parts, or
3. various combinations of these.

These three types cover all the form of the curve. Some examples will confirm this rule.

Curve--- geometric wave-like:
Equal radius---uniform alternation of positive and negative pressure.
Horizontal course with alternating tension and release.

Wassily Kandinsky 1866-1944, Point and Line to Plane (p.85)
Dover Books on Art and Art History