Zero of a Function

Zero of a Function

 

a point where a given function f(z) vanishes. Thus the zeros of the function f(z) are the same as the roots of the equation f(z) = 0. For example, the points 0, π, – π, 2π, – 2π, … are zeros of the function sin z.

The zeros of an analytic function f(z) are isolated points. For each such zero z0 there is a natural number k such that f (z0) = O, f′(z0) = 0, …, f(k-1) (z0) = 0, but fk(z0) ≠ 0; k is called the order of the zero. Thus for the zero of the function 1 – cos Φ, the order k = 2. A zero is said to be simple if k = 1, and multiple if k > 1.