Modal analysis has become an essential tool to understand the coherent structure of complex flows. The classical modal analysis methods, such as dynamic mode decomposition (DMD) and spectral proper orthogonal decomposition (SPOD), rely on a sufficient amount of data that is regularly sampled in time. However, often one needs to deal with sparse temporally irregular data, e.g., due to experimental measurements and simulation algorithm. To overcome the limitations of data scarcity and irregular sampling, we propose a novel modal analysis technique using multi-variate Gaussian process regression (MVGPR). We first establish the connection between MVGPR and the existing modal analysis techniques, DMD and SPOD, from a linear system identification perspective. Next, leveraging this connection, we develop a MVGPR-based modal analysis technique that addresses the aforementioned limitations. The capability of MVGPR is endowed by its judiciously designed kernel structure for correlation function, that is derived from the assumed linear dynamics. Subsequently, the proposed MVGPR method is benchmarked against DMD and SPOD on a range of examples, from academic and synthesized data to unsteady airfoil aerodynamics. The results demonstrate MVGPR as a promising alternative to classical modal analysis methods, especially in the scenario of scarce and temporally irregular data.

In reinforcement learning (RL), we always expect the agent to explore as many states as possible in the initial stage of training and exploit the explored information in the subsequent stage to discover the most returnable trajectory. Based on this principle, in this paper, we soften the proximal policy optimization by introducing the entropy and dynamically setting the temperature coefficient to balance the opportunity of exploration and exploitation. While maximizing the expected reward, the agent will also seek other trajectories to avoid the local optimal policy. Nevertheless, the increase of randomness induced by entropy will reduce the train speed in the early stage. Integrating the temporal-difference (TD) method and the general advantage estimator (GAE), we propose the dual-track advantage estimator (DTAE) to accelerate the convergence of value functions and further enhance the performance of the algorithm. Compared with other on-policy RL algorithms on the Mujoco environment, the proposed method not only significantly speeds up the training but also achieves the most advanced results in cumulative return.

Invento CEO Balaji Vishwanathan (right) and an employee interact with Spod, next to MITRI, a humanoid developed by the firm. At an office in HSR Layout, a box-shaped robot, mounted with a tablet, moves along the office floor while avoiding objects. As it detects a human face, it stops to greet and introduce itself: "Greetings, I'm Spod. I'm here to help you shop." Spod is an artificial intelligence-enabled robotic shopping assistant that visitors to supermarkets may well see in near future.

By Tushar Kaushik IN YOUR CART AI-enabled shopping assistant Spod can suggest products based on customer's age, gender. At an office in HSR Layout, a boxshaped robot, mounted with a tablet, moves along the office floor while avoiding objects. As it detects a human face, it stops to greet and introduce itself: "Greetings, I'm Spod. I'm here to help you shop." Spod is an artificial intelligence-enabled robotic shopping assistant that visitors to supermarkets may well see in near future.