Fixed-point iteration - Wikipedia
https://en.wikipedia.org/wiki/Fixed-point_iterationThe speed of convergence of the iteration sequence can be increased by using a convergence acceleration method such as Aitken's delta-squared process. The application of Aitken's method to fixed-point iteration is known as Steffensen's method, and it can be shown that Steffensen's method yields a rate of convergence that is at least quadratic.