We consider the problem of estimating the slope parameter in circular functional linear regression, where scalar responses Y 1, ..., Y n are modeled in dependence of 1-periodic, second order stationary random functions X 1, ...,X n . We consider an orthogonal series estimator of the slope function β, by replacing the first m theoretical coefficients of its development in the trigonometric basis by adequate estimators. We propose a model selection procedure for m in a set of admissible values, by defining a contrast function minimized by our estimator and a theoretical penalty function; this first step assumes the degree of ill-posedness to be known. Then we generalize the procedure to a random set of admissible m’s and a random penalty function. The resulting estimator is completely data driven and reaches automatically what is known to be the optimal minimax rate of convergence, in terms of a general weighted L 2-risk. This means that we provide adaptive estimators of both β and its derivatives.
Comte, F., & Johannes, J. (2010). Adaptive estimation in circular functional linear models. Mathematical Methods of Statistics, 19(1), 42-63. https://doi.org/10.3103/S1066530710010035 (Original work published 2010)