Irrational rotation
In the mathematical theory of dynamical systems, an irrational rotation is a map T θ : [ 0 , 1 ] → [ 0 , 1 ] , T θ ( x ) ≜ x + θ mod 1 , {\displaystyle T_{\theta }:[0,1]\rightarrow [0,1],\quad T_{\theta }(x)\triangleq x+\theta \mod 1,} where θ is an irrational number. Under the identification of a circle with R/Z, or with the interval [0, 1] with the boundary points glued together, this map becomes a rotation of a circle by a proportion θ of a full revolution (i.e., an angle of 2πθ radians).