The Yukawa Laboratory at the Department of Electronics and Electrical Engineering, Faculty of Science and Technology, Keio University, takes a mathematical approach to signal processing engineering. This field is a foundational technology at the heart of the electronics industry and an essential elemental technology for our information-based society. Aiming to create new value by extracting useful information from signals present in all phenomena, signal processing engineering is also used as a source technology for fields like big data analysis and brain-machine interfaces, which have recently attracted significant attention in industry.