# Rate of convergence of double sequences

Suppose $\{X_{n,m} \}$ be a double sequence of real numbers and suppose $\lim_{n}\lim_{m}X_{n,m}=X$. What is the definition and reference for the rate of convergence of double sequences?

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I added the tags "definition" and "reference-request". –  Alex Becker Dec 28 '11 at 19:30