Solved – the difference between corAR1 and corCAR1 correlation structures

I'm fitting a mixed multilevel model in R using the nlme package, and I don't understand what is the difference between the covariance structures corAR1 and corCAR1. Can someone help me?

Adding an answer because this question was never directly answered and I came here looking for the answer. Looking at the NLME documentation, corAR1 represents an autocorrelation structure of order 1. The corCAR1 argument represents an autocorrelation structure of order 1, with a continuous time covariate. In addition, Singer and Willet (2003) note the important distinction is that corCAR1 allows for unequally spaced time covariates or observations, while corAR1 requires equally spaced time intervals.

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