# Clarification in definition of Holt-Winters algorithm

The algorithm mentioned on Wikipedia has a line $$s_t = \alpha \frac{x_t}{c_{t-L}} + (1-\alpha) (s_{t-1} + b_{t-1})$$.

For $1 < t < L$ how should we interpret $c_{t-L}$? On that interval, should we replace it with $c_t$?

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Thanks, seems like we initialize $c_1 ... c_L$ in a certain way. Suppose there are 10 whole periods with $L = 10$ so 100 data points. After we initialize $c_1 ... c_{10}$, how do we compute $s_1$, which is a function of $c_{-9}$? – JCWong Aug 28 '12 at 3:32
The index $t$ is not understood modulo $L$. Use initial estimates as explained on the NIST site. – whuber Aug 28 '12 at 15:37