From plummer@iarc.fr  Thu Jul 22 11:26:41 1999
From: plummer@iarc.fr (Martyn Plummer)
Date: Thu, 22 Jul 1999 12:26:41 +0200 (CEST)
Subject: time series in R
In-Reply-To: <199907200932.LAA25315@sophie.ethz.ch>
Message-ID: <XFMail.990722122641.plummer@iarc.fr>

On 20-Jul-99 Martin Maechler wrote:
> 
> Something which should be discussed however is spectrum(0);
> Several of us think that S-plus does the wrong thing, at least in some
> cases. If  demean=T (mean removed),  should have periodogram(0) = 0,
> and maybe even spectrum(0) = 0 [and hence dB-spec. = -Inf ..]
> Another possibility would be to leave it NA

[I'm repeating some private discussions with Martin here]

In my version of spec.pgram(), I chose to ignore frequency zero. This
seemed like the right thing to do since the periodogram at zero does
not estimate the spectral density at zero, but is a function of the
mean. It does not make much sense to use this value when smoothing the
periodogram to estimate frequencies near zero. This remains true if you
decide to set periodogram(0)=0.

> and maybe provide methods for estimating it specifically, if desired.

I'm going to do this in the next version of the coda package.

Martyn
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time series in R
Martyn Plummer