Obsidian/Zettelkasten/Permanent Notes/20251223165340-mealy-machines.md
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---
id: 20251223165340
title: Mealy Machines
type: permanent
created: 2025-12-23T21:53:40Z
modified: 2025-12-23T22:38:18Z
tags: []
---
# Mealy Machines
Mealy machines are a formalization of a system that has
states drawn as nodes and transitions drawn from state to
state.
From Wikipedia:
```
A mealy machine is a finite state machine whose
output values are determined by both its current state, and
the current inputs.
```
Mealy machines can also be defined as a six-tuple:
$$(S, S_0, \Sigma, \Lambda, T, G)$$
where
- S is the finite set of states
- S_0 is the start state
- $\Sigma$ is the input alphabet
- $\Lambda$ is the output alphabet
- $T : S \times \Sigma \rightarrow S$ is the state
transition function
- $G : S \times \Sigma \rightarrow \Lambda$ is the output
function
Mealy machines have the advantage that they generally can
produce smaller sized automata (aka less states). This is
because transitions themselves in a Mealy machine are states
in a Moore machine. The state of 'opening' in a Moore
machine is the transition itself in a Mealy machine. Outputs
aren't just based on state, so it isn't necesary to create a
state to produce an output like a Moore machine. An output
action can be created with the current state AND the input
together.
## Related
[[Finite State Machines]]