1
Pushdown Stack Automata
Docsity.com
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community
Ask the community for help and clear up your study doubts
University Rankings
Discover the best universities in your country according to Docsity users
Free resources
Our save-the-student-ebooks!
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
From Context-Free Grammars to Pushdown Automata: Understanding the Process, Slides of Computer Science
How to convert context-free grammars (cfgs) into pushdown automata (pdas), a type of automaton used to recognize the languages defined by cfgs. The process involves recognizing recursive procedures in cfgs and carrying out recursive computations on a stack. The document also provides examples and instructions on how to recognize certain strings using a stack.
Typology: Slides
2012/2013
1 / 45
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download From Context-Free Grammars to Pushdown Automata: Understanding the Process and more Slides Computer Science in PDF only on Docsity!
1
Pushdown Stack Automata
2
Agenda
Pushdown Automata
Stacks and recursiveness
Formal Definition
18
By general principles, can carry out any
recursive computation on a stack. Can do it on a restricted version of an activation record stack, called a “ P ush d own (Stack) A utomaton” or PDA for short.
Q: What is the language generated by
S # | aSa | bSb?
19
A: Palindromes in {a,b,#}* containing
exactly one #-symbol.
Q: Using a stack, how can we recognize
such strings?
21
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
22
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
Input:
aaab#baa
24
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
a a
Input:
aaab#baa
25
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
a a a
Input:
aaab#baa
27
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
b a a a
Input:
aaab#baa
28
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
a a a
Input:
aaab#baa
30
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
a
Input:
aaab#baa REJECT (nonempty stack)
31
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
a a
Input:
aaab#baaa
33
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
Input:
aaab#baaa Pause input
34
PUSH
POP
read a or b?
Push it
ACCEPT
read #? (ignore stack)
read == peek? Pop Else: CRASH!
empty stack?
Input:
aaab#baaa ACCEPT