[R] spec.pgram returns different spectra when fast=TRUE and the number of samples is odd

[Duncan Murdoch]

Just curious:  did you read the help page to see what the "fast" 
argument does?  If you did, why are you surprised at this result?

Duncan Murdoch

On 19/10/2020 1:53 p.m., Jade Mosley via R-help wrote:
> Dear all,
> 
> This is potentially a bug in spec.pgram, when the number of samples is odd,spec.pgramreturns a different result withfast = TRUE, the example below contains the two varieties with a reference spectrum calculated manually. the number of returned spectra is also larger (50 compared to 49) whenfast = TRUE
> 
> x <- rnorm(
> 
> 99
> 
> )
> plot(spec.pgram(x, taper =
> 
> 0
> 
> , detrend =
> 
> FALSE
> 
> , plot =
> 
> FALSE
> 
> , fast =
> 
> FALSE
> 
> )$spec, ty =
> 
> 'l'
> 
> )
> lines(spec.pgram(x, taper =
> 
> 0
> 
> , detrend =
> 
> FALSE
> 
> ,plot =
> 
> FALSE
> 
> , fast =
> 
> TRUE
> 
> )$spec, col =
> 
> 'red'
> 
> )
> lines(((abs(fft(x))^
> 
> 2
> 
> )[
> 
> 2
> 
> :
> 
> 50
> 
> ])/
> 
> 99
> 
> , col =
> 
> 'blue'
> 
> , lty =
> 
> 2
> 
> )
> 
> Best regards
> 	[[alternative HTML version deleted]]
> 
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