6

Pushdown Automata

6.1 BASICS OF PUSHDOWN AUTOMATA

Q. What is Pushdown Automata? Describe the Block diagram or Mechanical diagram of Pushdown Automata. Why is it so named 'Pushdown'?

Ans. Pushdown Automata (PDA) is the machine format of context free language (CFL). It is one type of finite state machine (FSM) which is used to accept only CFLs.

Mechanical diagram:

images

(a) Input Tape: Input tape contains the input symbols. The tape is divided into a number of squares. Each square contains a single input character. The string placed in the input tape is traversed from left to right. Two end sides of the input string contain infinite number of blank ...

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