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2π ≠ 1
Chap 13: Introduction to Spectral Analysis
Spectral analysis has many important uses, e.g. using the residual
series to check on the white noise assumption of the error series.
Its use leads to a much broader alternative than the use of the acf
The spectral density, S(f), is defined by
Notice that S(f) is constant for white noise.
Some basic definitions,
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t=1:96; cos1=cos(2*pi*t*4/96); cos2=cos(2*pi*(t*14/96+.3))
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2*cos1 + 3*cos 2
The cosine model may be written in linear form,
Historical approximation for time series data,
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The Fourier frequencies.
fj = j/n
The periodogram.
Height of periodogram shows relative strength of cosine-sine pairs at
frequencies, f = j/n,, in overall behavior of series, {Yj}.
An identity, a decomposition
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Signal plus noise model. random signal case
A, B, W ~ IN(0,1)
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Hidden frequencies.
f unknown
look for maxima of periodogram
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The Spectral Representation.
If
A j , B j ~ IN(0, σ j 2 )
then
Rewrite
Cp. representing discrete r.v. by cdf.
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The sample spectral density.
Inverse relation
The spectral density.
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An Example
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