Regular expression
- Regular expression is a sequence of pattern that defines a string. It is used to denote regular languages.
- It is also used to match character combinations in strings. String searching algorithm used this pattern to find the operations on string.
- In regular expression, x* means zero or more occurrence of x. It can generate {e, x, xx, xxx, xxxx,.....}
- In regular expression, x+ means one or more occurrence of x. It can generate {x, xx, xxx, xxxx,.....}
Operations on Regular Language
The various operations on regular language are:
Union: If L and M are two regular languages then their union L U M is also a union.
L U M = {s | s is in L or s is in M}
Intersection: If L and M are two regular languages then their intersection is also an intersection.
L ⋂ M = {st | s is in L and t is in M}
Kleene closure: If L is a regular language then its kleene closure L1* will also be a regular language.
L* = Zero or more occurrence of language L.
Example
Write the regular expression for the language:
L = {abn w:n ≥ 3, w ∈ (a,b)+}
Solution:
The string of language L starts with "a" followed by atleast three b's. Itcontains atleast one "a" or one "b" that is string are like abbba, abbbbbba, abbbbbbbb, abbbb.....a
So regular expression is:
r= ab3b* (a+b)+
Here + is a positive closure i.e. (a+b)+ = (a+b)* - ∈
0 Comments