|
A Neumann series is a mathematical series of the form : where ''T'' is an operator. Hence, ''Tk'' is a mathematical notation for ''k'' consecutive operations of the operator ''T''. This generalizes the geometric series. The series is named after the mathematician Carl Neumann, who used it in 1877 in the context of potential theory. The Neumann series is used in functional analysis. It forms the basis of the Liouville-Neumann series, which is used to solve Fredholm integral equations. It is also important when studying the spectrum of bounded operators. == Properties == Suppose that ''T'' is a bounded operator on the normed vector space ''X''. If the Neumann series converges in the operator norm, then Id – ''T'' is invertible and its inverse is the series: :, where is the identity operator in ''X''. To see why, consider the partial sums :. Then we have : This result on operators is analogous to geometric series in , in which we find that: : One case in which convergence is guaranteed is when ''X'' is a Banach space and |''T''| < 1 in the operator norm. However, there are also results which give weaker conditions under which the series converges. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Neumann series」の詳細全文を読む スポンサード リンク
|