ACIT4330-Page/content/Definitions/Cauchy Sequence.md
2025-03-01 14:26:36 +01:00

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Definition

A Cauchy sequence is a sequence where the elements become arbitrarily close to each other as the sequence progresses.

Examples

Cauchy Sequence

\Sigma_{n=1}^\infty \frac{1}{n^2} = 1, \, \frac{1}{4}, \, \frac{1}{9}, \, \dots \lim_{ n \to \infty } \frac{1}{n^2} = 0

Which this sequence converges to 0, towards infinity

Non-Cauchy Sequence

\Sigma_{n=1}^{\infty}(-1)^n = -1, \, 1, \, -1, \, 1, \, \dots

These never converge to a limit, hence it is not Cauchy.

Furthermore, here, using something like \lim_{ n \to \infty } (-1)^n is nearly impossible to know what the value would be as \infty is neither even or odd.