A macron is a bar placed over a single symbol or character, such as 
. The symbol 
is sometimes used to denote the following operations:
1. The complex conjugate 
.
2. The mean 
(a.k.a. arithmetic mean)
of a set of values 
.
3. Negation of a logical expression.
4. Infrequently, the adjoint operator.
A bar placed over multiple symbols or characters is called a vinculum.
See also
Adjoint, Arithmetic Mean, Bar, Complex Conjugate, Hat, Mean, Vinculum
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References
Bringhurst, R. The Elements of Typographic Style, 2nd ed. Point Roberts, WA: Hartley and Marks, p. 281, 1997.
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Cite this as:
Weisstein, Eric W. "Macron." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Macron.html