Semiparametric Spatiotemporal Model with Mixed Frequencies // Fits a semiparametric spatiotemporal model for data with mixed frequencies, specifically where the response variable is observed at a lower frequency than some covariates. The estimation uses an iterative backfitting algorithm that combines a non-parametric smoothing spline for high-frequency data, parametric estimation for low-frequency and spatial neighborhood effects, and an autoregressive error structure. Methodology based on Malabanan, Lansangan, and Barrios (2022) h ttps://scienggj.org/2022/SciEnggJ%202022-vol15-no02-p90-107- Malabanan%20et%20al.pdf.