Simultaneous Registration and Clustering for Multidimensional Functional Data

The clustering for functional data with misaligned problems has drawn much attention in the last decade. Most methods do the clustering after those functional data being registered and there has been little research using both functional and scalar variables. In this article, we propose a simultaneous registration and clustering model via two-level models, allowing the use of both types of variables and also allowing simultaneous registration and clustering. For the data collected from subjects in different groups, a Gaussian process functional regression model with time warping is used as the first level model; an allocation model depending on scalar variables is used as the second level model providing further information over the groups. The former carries out registration and modeling for the multidimensional functional data (two-dimensional curves) at the same time. This methodology is implemented using an EM algorithm, and is examined on both simulated data and real data. Supplementary materials for this article are available online.