Dear R Users,
I have a CO2 time series. I want to fit this series seasonal cycle and trend
with fourth harmonic function,
and then compute residuals.

I am doing something like:

file<-read.csv("co2data.csv")
names(file)
attach(file)
fit<-lm(co2~1+time+I(time^2)+sin(2*pi*time)+cos(2*pi*time)+sin(4*pi*time)+cos(4*pi*time)+
sin(6*pi*time)+cos(6*pi*time)+sin(8*pi*time)+cos(8*pi*time),data=file)

fit$residuals

# variable 'co2' is in ppmv and variable 'time' is in the form of decimal
time.

The problem is: when I plot above residuals vs. time, it still shows some
seasonal cycle with time.
SO, I doubt that I am doing something wrong.

Kindly help, how to fit correctly, a fourth harmonic function on CO2 which
is varying with variable 'time'.

Great thanks,

Regards,
Yogesh

-- 
Yogesh K. Tiwari (Dr.rer.nat),
Scientist,
Indian Institute of Tropical Meteorology,
Homi Bhabha Road,
Pashan,
Pune-411008
INDIA

Phone: 0091-99 2273 9513 (Cell)
        : 0091-20-258 93 600 (O) (Ext.250)
Fax    : 0091-20-258 93 825

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