Hi,

I wanted to understand exactly how acf and pacf works, so I tried to
calculate ac and pac manually. For ac, I used the standard acf formula:
acf(k) = sum(X(t)-Xbar)(X(t-k)-Xbar))/sum(X(t)-Xbar)^2. But for pac, I could
not figure out how to calculate it by hand. I understand that in both R and
EVIEWS, it is done using the Durbin-Levinson algorithm by the computer.
However, I don't understand exactly how the algorithm works just by looking
at the algorithm. Does anyone know if there is a short cut to calculate pac
by hand (or in a spreadsheet), or is it too complex of a procedure that a
computer is absolutely necessary? It seems that there should be a natural
relationship between ac and pac so that once ac is calculated, pac can be
easily calculated based on ac.
Thanks,

-- 
Tom

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