# In terms of model fitting
# both sets of variables are equivalent
x <- diff(log(AirPassengers))
sd <- seasonal.dummies(x)
fit1 <- lm(x ~ sd[,-1])
summary(fit1)
sc <- seasonal.cycles(x)
fit2 <- lm(x ~ sc)
summary(fit1)
all.equal(fitted(fit1), fitted(fit2))
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