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In [[mathematics]], '''Cutler's bar notation''' is a [[Mathematical notation|notation system]] for [[large number]]s, introduced by Mark Cutler in 2004.  The idea is based on [[iterated exponentiation]] in much the same way that [[exponentiation]] is [[iteration|iterated]] [[multiplication]].
 
==Introduction==
A regular [[exponentiation|exponential]] can be expressed as such:
 
:<math>
  \begin{matrix}
  a^b & = & \underbrace{a_{} \times a \times\dots \times a} \\
  & & b\mbox{ copies of }a
  \end{matrix}
</math>
 
However, these expressions become arbitrarily large when dealing with systems such as [[Knuth's up-arrow notation]].  Take the following:
 
:<math>
  \begin{matrix}
& \underbrace{a_{}^{a^{{}^{.\,^{.\,^{.\,^a}}}}}} &
\\ 
& b\mbox{ copies of }a
  \end{matrix}
</math>
 
Cutler's bar notation shifts these exponentials counterclockwise, forming <math>{^b} \bar a</math>.  A bar is placed above the variable to denote this change.  As such:
 
:<math>
  \begin{matrix}
{^b} \bar a = & \underbrace{a_{}^{a^{{}^{.\,^{.\,^{.\,^a}}}}}} &
\\ 
& b\mbox{ copies of }a
  \end{matrix}
</math>
 
This system becomes effective with multiple exponent, when regular denotation becomes too cumbersome.
 
:<math>
  \begin{matrix}
^{^b{b}} \bar a = & \underbrace{a_{}^{a^{{}^{.\,^{.\,^{.\,^a}}}}}} &
\\ 
& {{^b} \bar a}\mbox{ copies of }a
  \end{matrix}
</math>
 
At any time, this can be further shortened by rotating the exponential counter-clockwise once more.
 
:<math>
  \begin{matrix}
\underbrace{b_{}^{b^{{}^{.\,^{.\,^{.\,^b}}}}}}  \bar a = {_c} \bar a
\\ 
c \mbox{ copies of } b
  \end{matrix}
</math>
 
The same pattern could be iterated a fourth time, becoming <math>\bar a_{d}</math>.  For this reason, it is sometimes referred to as '''Cutler's circular notation'''.
 
==Advantages and drawbacks==
 
The Cutler Bar Notation can be used to easily express other notation systems in exponent form.  It also allows for a flexible summarisation of multiple copies of the same exponents, where any number of stacked exponents can be shfted counter-clockwise and shortened to a single variable. The Bar Notation also allows for farily rapid composure of very large numbers. For instance, the number <math>\bar {10}_{10}</math> would contain more than a [[googolplex]] digits, whilst remaining fairly simple to write with and remember.
 
However, the system reaches a problem when dealing with different exponents in a single expression. For instance, the expression <math> ^{a^{b^{b^{c}}}}</math> could not be summarised in Bar notation.  Additionally, the exponent can only be shifted thrice before it returns to its original position, making a five degree shift indistinguishable from a one degree shift.  Some have suggested using a double and triple bar in subsequent rotations, though this presents problems when dealing with ten and twenty degree shifts.
 
==See also==
*[[Mathematical notation]]
 
==References==
 
*Mark Cutler, ''Physical Infinity'', 2004
*[[Daniel Geisler]], ''[http://www.tetration.org/ tetration.org]''
*R. Knobel. "Exponentials Reiterated." ''[[American Mathematical Monthly]]'' '''88''', (1981)
 
[[Category:Mathematical notation]]
[[Category:Large numbers]]

Latest revision as of 20:12, 27 June 2014

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