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I was learning about the convergence in probability. I'm unsure if looking at the epsiolon-delta definitions below which captures better the convergence in probability correctly.

$$ \forall \epsilon,\delta>0 \quad \exists n>N \qquad S.T \qquad Pr(|X_n -X|>\epsilon)<\delta $$

$$\forall \epsilon>0\quad\exists n>N \qquad S.T \qquad Pr(|X_n -X|>\epsilon)=0 $$

Pavan C.
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1 Answers1

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The usual definition of convergence in probability is $$ X_n \to_{p} X \iff \forall \epsilon > 0, \lim_{n \to \infty} P(|X_n - X| > \epsilon) = 0 $$

The limit is the "basic real analysis" sequence definition, since $P(|X_n - X| > \epsilon)$ is just a sequence over $n \in \mathbb{N}$. So using that definition, we have

$$ \forall \epsilon > 0, \lim_{n \to \infty} P(|X_n - X| > \epsilon) = 0 \iff \forall \epsilon > 0, \forall \delta > 0, \exists N \in \mathbb{N} \; \text{s.t.} \; \forall n \geq N, P(|X_n - X| > \epsilon) < \delta $$

This matches basically with the first one you wrote.

Pavan C.
  • 1,727