 Linear convergence

An iteration of a map has linear convergence to its limit when its nonzero errors $e_k=x_k-\alpha$ satisfy $|e_{k+1}|/|e_k|\to \rho$ for some $0<\rho <1$. The error eventually shrinks by approximately the same factor at each step. This is exact order of convergence one, in contrast to quadratic convergence.