# Pushdown Automaton

A Pushdown Automaton is an automaton that employs a stack ADT.

**AKA:**PDA.**Context:**- It can range from being a Deterministic Pushdown Automata to being a Non-Deterministic Pushdown Automata.

**See:**Nested Stack Automaton, Automata Theory, Finite-State Machine, Turing Machine, Deterministic Context-Free Language, Context-Free Language, Parser, Stack (Abstract Data Type).

## References

### 2017

- (Wikipedia, 2017) ⇒ https://en.wikipedia.org/wiki/Pushdown_automaton Retrieved:2017-1-27.
- In computer science, a
**pushdown automaton**(**PDA**) is a type of automaton that employs a stack.Pushdown automata are used in theories about what can be computed by machines. They are more capable than finite-state machines but less capable than Turing machines.

Deterministic pushdown automata can recognize all deterministic context-free languages while nondeterministic ones can recognize all context-free languages, with the former often used in parser design.

The term "pushdown" refers to the fact that the stack can be regarded as being "pushed down" like a tray dispenser at a cafeteria, since the operations never work on elements other than the top element. A

**stack automaton**, by contrast, does allow access to and operations on deeper elements. Stack automata can recognize a strictly larger set of languages than pushdown automata.A nested stack automaton allows full access, and also allows stacked values to be entire sub-stacks rather than just single finite symbols.

- In computer science, a