## biography

Yu-Hong Yeung is a current post-doctoral research associate in the Department of Computer Science at Purdue University, under the supervision of Prof. Alex Pothen. He received his Ph.D. degree in computer science in 2017 and his M.S. degree in computer science from Purdue University in 2012 and his B.Eng. degree in computer engineering from the Hong Kong University of Science and Technology in 2006. His research interests includes numerical linear algebra optimization, graph theory and parallel computing. He also did researches in computer graphics in previous years and video codec and streaming during his undergraduate. He has worked at Pacific Northwest National Laboratory for summer internships in 2014-2016 for developing new algorithms to the power grid contingency analysis problem. Prior to coming to the United States, he has worked as an assistant software engineer at the HKUST-WebEx IT Institute for developing a streaming server for teleconferencing.

## teaching

He has been the teaching assistant of the following courses:

- Foundations of Computer Science
- Programming in C
- Introduction to the Analysis of Algorithms
- Data Communication and Computer Networks
- Algorithm Design, Analysis and Implementation
- Computational Geometry
- Introduction to Scientific Visualization

## research

Current projects

**A**ugmented **M**atrix Solver for **P**rincipal **S**ubmatrix Updates

Dynamic matrix systems appear in many real-life applications such as surgery simulation and power grid security analysis. Most often the incremental changes are small compared to the size of the problem. After such changes occur no matter how small they are, traditionally the matrix requires refactorization, which are computationally expensive for large systems or systems with large number of small changes. Augmented matrix formulations provide an efficient alternative to solving these problems by preserving the original matrix as a submatrix of the new system and capturing the changes in the augmented parts. Linear algebra and graph theory techniques are then used to solve for the solutions to the modified systems efficiently. Sparsity of the matrices and vectors are exploited and symmetry of the matrices can also be preserved.

Computational surgery requires interactive visualization of solid finite element models of organs and their deformations as they are being cut. An example is astigmatism surgery of the eye, with the cornea cut to restore the normal curvature of the eye in orthogonal directions. The computational challenge here is to provide 10-100 updates of a system of equations of involving the stiffness matrix of a large mesh consisting of hundreds of thousands of nodes and elements to enable the visualization. Results showed that the augmented matrix approach is capable of surgical simulations that could be used in a haptic or graphic simulator.
< Publications > | |

The operators of power grids are required by law to compute what happens to the grids when a single generator or transmission line goes down, so that they know the corrective action to take. The problem arises when we want to compute what happens to the grid when some number k of the generators or lines go down. Now the number of scenarios to consider increases even for a grid consisting of a few thousand nodes. The study of this problem is called contingency analysis. To make the computations more feasible within a reasonable amount of time, augmented matrix solver can be applied to reduce the computation time since each scenario only differs slightly from the normal case. Our results show that the linear approximate solutions can be computed in over hundred times speedups. Extension to full nonlinear systems are being studied.
< Publications > |

Former projects

Appearance Editing of Real-World Objects

Appearance editing offers a unique way to view visually altered objects with various appearances or visualizations. By carefully controlling how an object is illuminated using digital projectors, we obtain stereoscopic imagery for any number of observers with everything visible to the naked eye (i.e., no need for head-mounts or goggles). Such an ability is useful for various applications, including scientific visualization, virtual restoration of cultural heritage, and display systems.

## personal

###### hobbies

music, animes, movies, books, maps drawing, hiking, cooking

###### languages

English, Cantonese, Mandarin

###### programming

C/C++, MATLAB, HTML5, CSS3, JavaScript