Editing Turing machine (section)

==="State" diagrams===

{|class="wikitable"
|+ The table for the 3-state busy beaver ("P" = print/write a "1")
|-
! Tape symbol
! colspan="3" | Current state A
! colspan="3" | Current state B
! colspan="3" | Current state C
|-
|
| Write symbol
| Move tape
| Next state
| Write symbol
| Move tape
| Next state
| Write symbol
| Move tape
| Next state
|-
| ''0''
| P
| R
| ''B''
| P
| L
| ''A''
| P
| L
| ''B''
|-
| ''1''
| P
| L
| ''C''
| P
| R
| ''B''
| P
| R
| ''HALT''
|}

[[File:State diagram 3 state busy beaver 2B.svg|thumb|500px|right|The "3-state busy beaver" Turing machine in a [[finite-state machine|finite-state representation]]. Each circle represents a "state" of the table—an "m-configuration" or "instruction". "Direction" of a state ''transition'' is shown by an arrow. The label (e.g. ''0/P,R'') near the outgoing state (at the "tail" of the arrow) specifies the scanned symbol that causes a particular transition (e.g. ''0'') followed by a slash ''/'', followed by the subsequent "behaviors" of the machine, e.g. "''P'' ''print''" then move tape "''R'' ''right''". No general accepted format exists. The convention shown is after McClusky (1965), Booth (1967), Hill, and Peterson (1974).]]

To the right: the above table as expressed as a "state transition" diagram.

Usually large tables are better left as tables (Booth, p.&nbsp;74). They are more readily simulated by computer in tabular form (Booth, p.&nbsp;74). However, certain concepts—e.g. machines with "reset" states and machines with repeating patterns (cf. Hill and Peterson p.&nbsp;244ff)—can be more readily seen when viewed as a drawing.

Whether a drawing represents an improvement on its table must be decided by the reader for the particular context.

[[File:Moves of a 3-state Busy Beaver.jpg|thumbnail|500px|right|The evolution of the busy beaver's computation starts at the top and proceeds to the bottom.]]

The reader should again be cautioned that such diagrams represent a snapshot of their table frozen in time, ''not'' the course ("trajectory") of a computation ''through'' time and space. While every time the busy beaver machine "runs" it will always follow the same state-trajectory, this is not true for the "copy" machine that can be provided with variable input "parameters".

The diagram "progress of the computation" shows the three-state busy beaver's "state" (instruction) progress through its computation from start to finish. On the far right is the Turing "complete configuration" (Kleene "situation"<!-- Stuation? Not Situation? Is that the right word? Yes, it is, cf. page 375 for example "The Godel number of the stiuation..." and then he shows a tape, etc. This usage runs throughout the chapter. wvbailey~~~~ --><!--So is it "stuation" or "stiuation"?-->, Hopcroft–Ullman "instantaneous description") at each step. If the machine were to be stopped and cleared to blank both the "state register" and entire tape, these "configurations" could be used to rekindle a computation anywhere in its progress (cf. Turing (1936) ''The Undecidable'', pp.&nbsp;139–140).