# Wolfram Language & System 11.0 (2016)|Legacy Documentation

This is documentation for an earlier version of the Wolfram Language.
BUILT-IN WOLFRAM LANGUAGE SYMBOL

# SubstitutionSystem

SubstitutionSystem[rule,init,t]
generates a list representing the evolution of the substitution system with the specified rule from initial condition init for t steps.

SubstitutionSystem[rule,init]
gives the result of evolving init for one step.

SubstitutionSystem[rule]
is an operator form of SubstitutionSystem that corresponds to one step of evolution.

## DetailsDetails

• In SubstitutionSystem[rule,], rule can be of the following forms:
•  {i1rhs1,i2rhs2,…} list substitution system {"s1"rhs1,"s2"rhs2,…} string substitution system
• In list substitution systems, the rhsi can be lists of any length or can be rectangular arrays of any depth but all with the same dimensions. They can also be individual elements such as integers.
• In string substitution systems, the rhsi can be strings of any length.
• Both lists and string substitution systems can have rules that involve patterns, but every object that appears in the rhsi must have a transformation defined by the rules given.
• List substitution systems work with SparseArray objects.
• In string substitution systems, the initial condition init must be a string; in list substitution systems, it must be an array whose depth is equal to the depth of the rhsi.
• In SubstitutionSystem[rule,init,tspec], the time specification tspec can have any of the following forms:
•  t all steps 0 through t {t} a list containing only step t {t1,t2} steps t1 through t2 {t1,t2,dt} steps t1, t1+dt, …

## ExamplesExamplesopen allclose all

### Basic Examples  (3)Basic Examples  (3)

Five steps of a string substitution system:

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Analogous substitution system with lists:

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Steps in a 2D substitution system:

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Give the fourth step only:

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Alternative form:

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Generate a rule icon for a substitution system:

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