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Answers for “当没有前一期时,如何初始化第一个预测?”

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Because the recursive formula needs a previous forecast, the video demonstrates a simple initialization method: set the first forecast equal to the first actual observation. In the example this gives F(1)=A(1)=1103F(1)=A(1)=1103.

Conditions: Applies when no earlier forecast is available.; Shown specifically for Week 1 in the example.

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Within this clip, the setup is completed through the Week 2 formula and the recursion pattern for later weeks is explained; the numerical Week 11 forecast is not yet computed on screen.

Conditions: The clip ends after demonstrating the Week 2 formula entry.; The goal stated at the beginning is to find the Week 11 forecast.

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Alpha is defined in the video as the exponential smoothing constant. It multiplies the previous forecast error and determines the size of the adjustment added to the previous forecast.

Conditions: Treated as a given constant in the problem.; Held fixed across all periods in the example.

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The video presents the single-parameter exponential smoothing update rule. The new forecast equals the prior forecast plus a fraction alpha of the prior forecast error, where the error is measured as actual minus forecast from the previous period.

Conditions: Used recursively over discrete time periods.; Requires a starting forecast value.; In the example, alpha is supplied as 0.2.

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The video translates the mathematical recurrence into an Excel formula. For Week 2, the current forecast is computed from the Week 1 forecast in C4, the Week 1 actual in B4, and the smoothing constant in B2.

Conditions: Requires a table with actuals in one column and forecasts in another.; Uses relative references for prior row values and an absolute reference for alpha.