Holt-Winters Forecasting

[volomike]

Do you know how to use Holt-Winters Seasonal Dampened Method?

Scroll to the bottom of here:

http://otexts.com/fpp/7/5/

Now, knowing that, do you know how to make a forecast in PHP? See, I'm trying to do some sales charts in a PHP app I'm building. I have year 1 and year2 data, but year2 might be partial (less than 12 months) or complete (12 months). I need to simply use Holt-Winters Seasonal Dampened Method to compute 2 months sales forecast forward.

[volomike]

Looks like in your code comments you did provide a way to do a forecast. Sweet! So, anyway, I wanted to know how much this function have here differs from HW Seasonal Dampened Method, or is it just a matter of tweaking alpha, beta, and gamma?

[crirus]

Does this code work as intended? I tried with some values between 200 and 400 and the forecast jumped above 1300... I inputed two and a half seasons of 7 days.

Any hint appreciated...

[fiatux]

what should be the relation/ratio between data array count and season length? did anyone figure that out?

i guess this algorithm is trying to make an output for a season length long, i only need to next item.

[shieryntjandra]

After i studied holt winters exponential multiplicative, i just familiar with parameter alpha, gamma and beta. But in your code, suddenly dev_gamma has appear. Could you give me an explanation about parameter dev_gamma? where do i supposted to get that value?

[bagus86]

your website on phpir.com not aceess , i want to be a read your article bro :(