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Monotone convergence theorem

In mathematics, there are several theorems dubbed monotone convergence; here we present some major examples.

1) If ak is a monotone sequence of real numbers (e.g., if ak≤ak+1,) then this sequence has a limit (if we admit plus and minus infinity as possible limits.) The limit is finite if and only if the sequence is bounded.

2) If for each natural numbers j and k, aj,k is a non-negative real number, and furthermore, for each j,k, aj,k≤aj+1,k, then

\lim_{j\to\infty} \sum_k a_{j,k} = \sum_k \lim_{j\to\infty} a_{j,k}

3) If fk are non-negative measurable real-valued functions with measure μ such that for each k and x, fk(x)≤fk+1(x), then

\lim_{k\to\infty} \int f_k(x)d\mu(x) = \int\lim_{k\to\infty} f_k(x)d\mu(x)

This theorem generalizes the previous one. It is sometimes called the Lebesgue monotone convergence theorem; and is probably the most important monotone convergence theorem.

See also: infinite series.

01-04-2007 01:18:14
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