Editing Probabilistic Turing machine (section)

{{Short description|Mathematical model of computation}}
{{Use dmy dates|date=May 2020}}
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In [[theoretical computer science]], a '''probabilistic Turing machine''' is a [[non-deterministic Turing machine]] that chooses between the available [[State-transition table|transitions]] at each point according to some [[probability distribution]]. As a consequence, a probabilistic Turing machine can (unlike a deterministic Turing machine) have [[stochastic]] results; that is, on a given input and instruction state machine, it may have different run times, or it may not halt at all; furthermore, it may accept an input in one execution and reject the same input in another execution.

In the case of equal probabilities for the transitions, probabilistic Turing machines can be defined as deterministic [[Turing machine]]s having an additional "write" instruction where the value of the write is [[uniform distribution (discrete)|uniformly distributed]] in the Turing machine's alphabet (generally, an equal likelihood of writing a "1" or a "0" on to the tape). Another common reformulation is simply a [[deterministic Turing machine]] with an added tape full of random bits called the "random tape".

A [[quantum computer]] (or [[quantum Turing machine]]) is another [[model of computation]] that is inherently [[probabilistic]].