Editing Circumflex (section)

===Mathematics===
{{main|Hat notation}}
In mathematics, the circumflex is used to modify variable names; it is usually read "hat", e.g., <math>\hat x</math> is "x hat". The [[Fourier transform]] of a function ''ƒ'' is often denoted by <math>\hat f</math>.

In geometry, a hat is sometimes used for an [[angle]]. For instance, the angles <math>\hat{A}</math> or <math>\widehat{ABC}</math>.

In vector notation, a hat above a letter indicates a [[unit vector]] (a dimensionless [[vector (geometric)|vector]] with a [[Magnitude (mathematics)|magnitude]] of 1). For instance, <math>\hat{\mathbf{\imath}}</math>, <math>\hat{\mathbf{x}}</math>, or <math>\hat{\mathbf{e}}_1</math> stands for a unit vector in the direction of the [[x-axis]] of a [[Cartesian coordinate system]].

In [[statistics]], the hat is used to denote an [[estimator]] or an estimated value, as opposed to its theoretical counterpart. For example, in [[errors and residuals]], the hat in <math>\hat\varepsilon</math> indicates an observable estimate (the residual) of an unobservable quantity called <math>\varepsilon</math> (the statistical error). It is read ''x-hat'' or ''x-roof'', where ''x'' represents the character under the hat.