Jade Mosley
2020-Oct-19 17:53 UTC
[R] spec.pgram returns different spectra when fast=TRUE and the number of samples is odd
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]]
Duncan Murdoch
2020-Oct-19 20:11 UTC
[R] spec.pgram returns different spectra when fast=TRUE and the number of samples is odd
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]] > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >