Forward Problem From the axiom, use the production rules to genreate the desired number of steps. With the geometric interpretations of the alphabet, draw the figure defined by the string. Alternately, assemble a figure consisting of a small number of steps with twist-ties (these bend easily and keep their shape). Then build figures consisting of a larger number of steps by assembling copies of the twist-tie figures.
With L-System software this is much simpler: enter the axiom, production rules, turning angle, and number of steps. Then run the program.
Inverse Problem Given a figure, find the axiom and production rules that generate the figure. Generally, many combinations of axioms and production rules can yield a given figure, and some of these will disagree on later steps. So we settle for a simpler problem. Given two (consecutive, early) steps, find the axiom and production rule. This is a pattern-recognition problem; it becomes easier with practice.
Return to L-Systems: Patterns with Grammar