Volume I: Mathematical Analysis was published in June 2017 by SIAM. You can purchase your copy here http://bookstore.siam.org/ot152/.
Volume II: Algorithms, Approximation, Optimization will be published in 2019 by SIAM. A preliminary copy of this textbook is available for purchase through the math department to registered students.
Volume III: Modeling Uncertainty with Data and Volume IV: Modeling with Dynamics and Control are still under development, but are expected to publish in 2021. Materials for these classes will be distributed as needed.