先看一下定理描述:
Theorem 1.1: Let (, ) be a complete metric space and be a map such that for some and all and in . Then has a unique fixed point in . Moreover, for any the sequence of iterates , , , ...... converges to the fixed point of .
When for some and all and in , is called a contraction. A contraction shrinks distances by a uniform factor less than 1 for all pairs of points. Theorem 1.1 is called the contraction mapping theorem or Banach’s fixed-point theorem.
也就是說:
定義尺度空間(, ) (可理解爲空間中元素,爲空間距離度量) 以及映射函數 (函數輸入是尺度空間中的元素,輸出仍然屬於該空間),如果存在, ,使得 成立,則函數在中具有唯一不動點。此外,對於任意,序列, , 收斂至的不動點
稱爲contraction(壓縮)函數。定理1.1稱爲 contraction mapping 定理或巴拿赫不動點定理
上述材料來源於[1]
簡單明瞭的介紹:
[1]. http://www.math.uconn.edu/~kconrad/blurbs/analysis/contraction.pdf
[2]. http://mathonline.wikidot.com/banach-s-fixed-point-theorem
此外,更豐富的鏈接:
1. 知乎,Banach空間和不動點定理 : https://zhuanlan.zhihu.com/p/26346061
2. 知乎,如何理解不動點定理?: https://www.zhihu.com/question/21835995