Editing L-system (section)

===Stochastic grammars===
The grammar model we have discussed thus far has been deterministic—that is, given any symbol in the grammar's alphabet, there has been exactly one production rule, which is always chosen, and always performs the same conversion. One alternative is to specify more than one production rule for a symbol, giving each a [[probability]] of occurring. For example, in the grammar of Example 2, we could change the rule for rewriting "0" from:

:0 → 1[0]0

to a probabilistic rule:

:0 (0.5) → 1[0]0
:0 (0.5) → 0

Under this production, whenever a "0" is encountered during string rewriting, there would be a 50% chance it would behave as previously described, and a 50% chance it would not change during production. When a stochastic grammar is used in an [[evolution]]ary context, it is advisable to incorporate a [[random]] seed into the [[genotype]], so that the stochastic properties of the image remain constant between generations.