The ATLAS Penalty: Auxiliary-Transformed Location-Aware Smoothing with Applications to Spatial Transcriptomics
We address the problem of fitting a collection of location-specific models under a spatial smoothness assumption. Existing approaches penalize roughness in the model parameters directly, an assumption that breaks down when smoothness is a function of parameters and auxiliary covariates rather than the parameters themselves. Our framework, the Auxiliary-Transformed Location-Aware Smoothing (ATLAS) penalty, generalizes spatial smoothness by penalizing roughness in transformations of model parameters using auxiliary information. As a concrete case study, we develop a spatially smooth deconvolution model for spatial transcriptomics that estimates tumor mixing coefficients from thousands of spots distributed on a single tissue slide. To handle the computational challenges posed by the nonlinear likelihood, nonsmooth nonconvex penalty, and spatially coupled estimation, we propose an alternating direction method of multipliers (ADMM) algorithm. Through simulation studies, we demonstrate that our framework provides substantially better spatial domain detection than approaches that smooth model parameters directly, with particularly strong gains when auxiliary covariates carry calibrated spatial structure.