In mathematics, a quasiperiodic function is a function that has a certain similarity to a periodic function. A function is quasiperiodic with quasiperiod if , where is a "simpler" function than . What it means to be "simpler" is vague. A simple case (sometimes called arithmetic quasiperiodic) is if the function obeys the equation: Another case (sometimes called geometric quasiperiodic) is if the function obeys the equation: An example of this is the Jacobi theta function, where Functions with an additive functional equation