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Pushdown autometa
Pushdown automata are a new form of finite automata that have increased language recognition capabilities through the addition of a pushdown stack. A pushdown automaton is defined by an input alphabet, input tape, stack alphabet, pushdown stack, start state, halt states, push states, and read states. It can perform push and pop operations on the stack to recognize nested or hierarchical language structures that regular finite automata cannot. The addition of a stack allows pushdown automata to recognize context-free languages while retaining the intuitive graphical representation of finite automata.
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Pushdown autometa
- 1. Pushdown Automata A NEWFORM OF FA’S
- 2. Terms To Know: InputTape Pictorial Representation Start Reject Accept Read Example Stack Pushdown Automata
- 3. Input Tape The Partof FA where the input lives is called Input Tape The Location is which we put input letter is called cells
- 4. Example Of InputTape The Example of tape that contain some of our input letter Here ∆ is used to indicate the blank in the tape cell Means that this cell is empty and we can place a letter into this cell
- 5. Input Tape: Properties As weprocess the tape onto the machine We read one letter a time After reading the letter we will eliminate that letter assuming that it is used When we will read first blank cell we will stop because we will assume that after first blank cell all other cells will also be blank And we read cells from Left To Right
- 6. Start / Reject/ Accept A start State is a state from where we begin the process but read inputs no letter Start A start state has no arrow coming into it A reject state Is dead-end non final state, where all the input is consumed but we did not achieve the goal Reject A Accept state is a dead-end a final state tells that the input is accepted and we have achieved our goal Accept
- 7. Read State We arechanging our diagrams so an important thing in our FA’s was to read a letter and then decide where to go so in pictorial representation we have introduced a READ state. Read state is just like a diamond shape.
- 8. Remember When the character∆ is read from input tape means that we are out of input Then we Finish Processing The ∆-edge will lead us to accept state if the state have stop into final Other wise it will lead us to reject state In old methods we have no idea when we are out of inputs
- 9. Example: Convert FA toPictorial Representation:
- 10. What is thebenefit???? It just like flow chart so what is the reason to use this and Using Pictorial representation we still representation the FA’s so how can we give more power to our machine????? For this purpose we will use the “STACK” It is easy to use stack with these pictorial representation
- 11. Stack: Push Down Stack/Push Down Store A stack is a storage point where we can store our input letter And then call them back when we will refer it Stack Pointer: That point the top of the stack It has two main Operations Push POP
- 12. PDA: Push Down Automata WhenFA’s have been souped up with the Stack Push Pop Then we call it the push down automata abbreviated as PDA’s By adding this data structure the language recognizing capability is increased.
- 13. How To Definea PDA A push down automata is collection of 8 things An alphabet ∑ (Segma)of input letters An input Tape An Alphabet (Taa) of stack character A pushdown stack On start State Halt States Push State Read State State Read Top of stack