Lefschetz zeta function


In mathematics, the Lefschetz zeta-function is a tool used in topological periodic and fixed point theory, and dynamical systems. Given a continuous map, the zeta-function is defined as the formal series
where is the Lefschetz number of the -th iterate of. This zeta-function is of note in topological periodic point theory because it is a single invariant containing information about all iterates of.

Examples

The identity map on has Lefschetz zeta function
where is the Euler characteristic of, i.e., the Lefschetz number of the identity map.
For a less trivial example, let be the unit circle, and let be reflection in the x-axis, that is,. Then has Lefschetz number 2, while is the identity map, which has Lefschetz number 0. Likewise, all odd iterates have Lefschetz number 2, while all even iterates have Lefschetz number 0. Therefore, the zeta function of is

Formula

If f is a continuous map on a compact manifold X of dimension n, the zeta function is given by the formula
Thus it is a rational function. The polynomials occurring in the numerator and denominator are essentially the characteristic polynomials of the map induced by f on the various homology spaces.

Connections

This generating function is essentially an algebraic form of the Artin–Mazur zeta function, which gives geometric information about the fixed and periodic points of f.