Yang, Yu2023-11-282023-11-282023-06https://hdl.handle.net/11299/258692University of Minnesota Ph.D. dissertation. May 2023. Major: Statistics. Advisor: Xiaotong Shen. 1 computer file (PDF); x, 132 pages.This doctoral thesis delves into the realms of abstractive summarization and causal discovery within complex systems. I present a set of new methods that counter prevailing challenges, uncovering the significant roles that topic awareness, normalizing flows, and hierarchical ensemble techniques can play in enhancing text summarization and causal discovery, respectively. The first part of the thesis investigates abstractive summarization, introducing PA-TAM, a model that employs a hierarchical approach to incorporate topic information at both document and sentence levels and a penalized attention mechanism to reduce textual repetitions. The application of these techniques results in the generation of coherent and informative summaries. Furthermore, I propose FlowSUM, a normalizing flows-based variational encoder-decoder framework tailored for Transformer-based summarization models. FlowSUM mitigates challenges related to capturing complex semantic structures and dealing with posterior collapse during training, thereby enriching the latent posterior distribution and improving summary quality. FlowSUM is also shown to possess great potential for transferring knowledge from large language models. The second part of the thesis focuses on causal discovery, particularly targeting the wafer manufacturing domain. I propose a hierarchical ensemble approach that leverages temporal and domain constraints, simultaneously handling challenges such as high-dimensional, mixed, and imbalanced data, as well as irregular missing patterns. The efficacy of this approach is substantiated through simulations and a real-world application to Seagate Technology's wafer manufacturing data, providing valuable insights for process optimization and real-time root cause tracing.encausal discoveryhierarchical ensemblenormalizing flowstext summarizationtopic awarenessThesis or Dissertation