Yamada, Makoto, and Masashi Sugiyama. “Direct Density-Ratio Estimation With Dimensionality Reduction via Hetero-Distributional Subspace Analysis”. Proceedings of the AAAI Conference on Artificial Intelligence 25, no. 1 (August 4, 2011): 549–554. Accessed May 7, 2026. https://ojs.aaai.org/index.php/AAAI/article/view/7905.