[R] help! - spectral analysis - spec.pgram

From: Nuno Prista <nmprista_at_fc.ul.pt>
Date: Thu, 27 Mar 2008 11:36:04 -0400


Can someone explain me this spec.pgram effect?  

Code:  

period.6<-c(0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10
,0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10,0,0,0,0,0,10)

period.5<-c(0,0,0,0,0,10,0,0,0,0,10,0,0,0,0,0,0,10,0,0,0,0,10,0,0,0,0,0,0,10
,0,0,0,0,10,0,0,0,0,0,0,10,0,0,0,0,10,0,0,0,0,0,0,10,0,0,0,0,10,0)
 

par(mfrow=c(2,1))  

spec.pgram(period.6, log="no")

spec.pgram(period.5, log="no")    

The first series has period 6 and shows its periodicity in 1/6 and harmonics. In the second series I was expecting to see a signal occurring at frequency 1/5 but it does not. Can anybody explain me why?  

Thanks in advance,  

Nuno  


Centro de Oceanografia - IO-FCUL, Portugal

Center for Quantitative Fisheries Ecology - ODU, USA

email: nmprista*@fc.ul.pt ; nprista*@odu.edu  

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