Principles of Programming Seminar

Friday, April 29, 2016 - 2:00pm


Traffic 21 Classroom 6501 Gates & Hillman Centers


THOMAS WAHL, Assistant Professor

The precise semantics of floating-point arithmetic programs depends on the execution platform, including the compiler and the target hardware.  Platform dependencies are particularly pronounced for arithmetic-intensive scientific numeric programs and infringe on the highly desirable goal of software portability (which is in fact promised by heterogeneous computing frameworks like OpenCL): the same program run on the same inputs on different platforms can produce different results. Serious doubts on the portability of numeric applications arise when these differences are behavioral, i.e. when they lead to changes in the control flow of a program. In this talk I will first present an algorithm that takes a numeric procedure and determines whether a given input can lead to different decisions depending merely on how the arithmetic in the procedure is compiled and executed. I will then show how this algorithm can be used in static and dynamic analyses of programs, to estimate their numeric stability. I will illustrate the results on examples characteristic of numeric computing where control flow divergence actually occurs across different execution platforms. — Thomas Wahl joined the faculty of Northeastern University in 2011. He moved to Boston from Oxford/United Kingdom, where he was a researcher in the Computing Laboratory (now Department of Computer Science).  Prior to the Oxford experience, Wahl held a postdoctoral position at the Swiss Federal Institute of Technology (ETH) in Zurich. He obtained a PhD degree in Computer Science from the University of Texas at Austin in 2007. Wahl's research concerns the reliability of complex and mission-critical computing systems. Two domains notorious for their fragility are concurrency and numerical computing. With colleagues, Wahl has developed leading algorithms and techniques that permit the automated analysis of concurrent software such as multi-threaded or data-parallel programs using rigorous formal techniques, which are able to track down deep, unintuitive and nearly untestable program bugs. He has also investigated how floating-point arithmetic can "hijack" a program's computation when run on non-standard architectures, such as heterogeneous and custom-made embedded platforms. Faculty Host: André Platzer

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