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Answers for “原始交叉熵方法的目的是什么?”

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The iteration threshold γi\gamma_i is defined as the empirical (1−p)(1-p)-quantile of the current batch of samples drawn from the proposal distribution. The loop stops when this threshold γi\gamma_i is greater than or equal to the target rare-event threshold γ\gamma.

Conditions: Samples are drawn from the current proposal distribution.; The elite fraction parameter pp is set to 0.05.; The target threshold is γ=5\gamma=5.

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The video states that the earlier example 'cheated' because the rare event was not very rare, making direct rejection sampling from g∗g^* computationally feasible. In general, for truly rare events, direct rejection sampling would take too long, which motivates the use of the adaptive cross-entropy method.

Conditions: The context is comparing the improved cross-entropy method to the original cross-entropy method.; The rare event in the earlier example had a relatively high probability.