Lets Recapitulate 1 Regular Languages DFAs NFAs Regular
- Slides: 53
Let’s Recapitulate 1
Regular Languages DFAs NFAs Regular Grammars Regular Expressions 2
A standard representation of a regular language : A DFA that accepts A NFA that accepts A regular expression that generates A regular grammar that generates 3
When we say: “We are given a Regular Language “ We mean: Language in a standard representation 4
Elementary Questions about Regular Languages 5
Question: Given regular language how can we check if a string ? 6
Question: Answer: Given regular language how can we check if a string ? Take the DFA that accepts and check if is accepted 7
Question: Answer: Given regular language how can we check if is empty, finite, infinite ? Take the DFA that accepts Then check the DFA 8
If there is a walk from the start state to a final state then: is not empty Otherwise empty If the walk contains a cycle then: is infinite Otherwise finite 9
Question: Given regular languages how can we check if and ? 10
Question: Given regular languages how can we check if and ? Answer: take And find if 11
Question: Given language how can we check if is not a regular language ? 12
Question: Given language how can we check if is not a regular language ? Answer: The answer is not obvious We need the Pumping Lemma 13
The Pigeonhole Principle 14
4 pigeons 3 pigeonholes 15
A pigeonhole must have two pigeons 16
pigeons. . . pigeonholes. . . 17
The Pigeonhole Principle pigeons pigeonholes There is a pigeonhole with at least 2 pigeons . . . 18
The Pigeonhole Principle and DFAs 19
DFA with states 20
In walks of strings: no state is repeated 21
In walks of strings: a state is repeated 22
If the walk of string has length Then a state is repeated 23
The pigeonhole principle: If in a walk: Then: transitions states A state is repeated 24
In other words: transitions are pigeons states are pigeonholes 25
In general: A string has length A state must be repeated in the walk . . . number of states . . . 26
The Pumping Lemma 27
Take an infinite regular language DFA that accepts states 28
Take string with There is a walk with label : . . 29
If string number of states has length Then, from the pigeonhole principle: A state is repeated in the walk . . . 30
Write . . . 31
Observations : number of states length . . . 32
Observation: The string . . . is accepted . . . 33
Observation: The string is accepted . . . 34
Observation: The string is accepted . . . 35
In General: The string is accepted . . . 36
In other words, we described: The Pumping Lemma 37
The Pumping Lemma: 1. Given a infinite regular language 2. There exists an integer 3. For any string with length 4. We can write 5. With and 6. Such that: string 38
Applications of the Pumping Lemma 39
Claim: The language is not regular Proof: Use the Pumping Lemma 40
Proof: Assume for contradiction that is a regular language Since is infinite we can apply the Pumping Lemma 41
Let be the integer in the Pumping Lemma Pick a string such that: length Example: pick 42
Write From the Pumping Lemma it must be that length Therefore: 43
From the Pumping Lemma: Thus: 44
Therefore, BUT: and CONTRADICTION!!! 45
Therefore: Our assumption that is a regular language cannot be true CONCLUSION: is not a regular language 46
Claim: The language is not regular Proof: Use the Pumping Lemma 47
Proof: Assume for contradiction that is a regular language Since is infinite we can apply the Pumping Lemma 48
Let be the integer in the Pumping Lemma Pick a string such that: length Example: pick 49
Write From the Pumping Lemma it must be that length Therefore: 50
From the Pumping Lemma: Thus: 51
Therefore, BUT: and CONTRADICTION!!! 52
Therefore: Our assumption that is a regular language cannot be true CONCLUSION: is not a regular language 53
- Nfas are ___ dfas.
- Verb to be
- Regular grammars generate regular languages.
- Dfas organizational chart
- Nih dfas
- Dfas fein
- Decision properties of regular languages
- Right linear grammar
- Cs
- Decision properties of regular languages
- Decision properties of regular languages
- Decision properties of regular language
- Properties of regular languages
- Closure properties of regular expression
- Regular and irregular languages
- Pumping lemma non regular languages examples
- What is internal benchmarking
- Let's watch a video
- Lets go hudro
- The word-skipping technique lets you figure out
- Let's reported speech
- Offercore nedir
- Let's spread the word
- Lets revisit
- The lets
- Lets review
- Get ready for
- 7 horse optical illusion answer
- Let's answer
- Lets remember
- Lets play bridge
- Let’s fight it together
- Lets see what you already know
- Progressive lets
- Lets make waves
- Evolution english language
- Youth unit
- Description of a person
- Lets livingston county
- Lets have a recap
- Company slogan here
- Lets get started images
- Lets move on
- Warm up questions about travelling
- Lets review cartoon
- Let's play jeopardy
- Paper that lets the light shine through
- Lets play
- Let's do the rooms
- Let's go lesson plans
- Let's clean together
- Lets see what you know
- Lets review
- We're free let's grow answer key