Minkowski's Question Mark Function - Recursive Definition For Rational Arguments

Recursive Definition For Rational Arguments

For rational numbers in the unit interval, the function may also be defined recursively; if p/q and r/s are reduced fractions such that | ps − rq | = 1 (so that they are adjacent elements of a row of the Farey sequence) then

Using the base cases

it is then possible to compute ?(x) for any rational x, starting with the Farey sequence of order 2, then 3, etc.

If and are two successive convergents of a continued fraction, then the matrix

has determinant ±1. Such a matrix is an element of, the group of two-by-two matrices with determinant ±1. This group is related to the modular group.

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