cosinor.lm {cosinor}  R Documentation 
Given an outcome and time variable, fit the cosinor model with optional covariate effects.
cosinor.lm(formula, period = 12, data, na.action = na.omit)
formula 
Forumla specifying the model. Indicate the time variable with

period 
Length of time for a complete period of the sine curve. 
data 
Data frame where variable can be found 
na.action 
What to do with missing data 
This defines special functions that are used in the formula to
indicate the time variable and which covariates effect the amplitude. To
indicate the time variable wrap the name of it in the function
time()
. To indicate a variable which affects the
acrophase/amplitude, wrap the name in amp.acro()
. This will then do
all the tranformations for you. See examples for usage.
Tong, YL. Parameter Estimation in Studying Circadian Rhythms, Biometrics (1976). 32(1):85–94.
cosinor.lm(Y ~ time(time) + X + amp.acro(X), data = vitamind)