Pushdown Control-Flow Analysis of Higher-Order Programs

Context-free approaches to static analysis gain precision over classical approaches by perfectly matching returns to call sites---a property that eliminates spurious interprocedural paths. Vardoulakis and Shivers's recent formulation of CFA2 showed that it is possible (if expensive) to apply context-free methods to higher-order languages and gain the same boost in precision achieved over first-order programs. To this young body of work on context-free analysis of higher-order programs, we contribute a pushdown control-flow analysis framework, which we derive as an abstract interpretation of a CESK machine with an unbounded stack. One instantiation of this framework marks the first polyvariant pushdown analysis of higher-order programs; another marks the first polynomial-time analysis. In the end, we arrive at a framework for control-flow analysis that can efficiently compute pushdown generalizations of classical control-flow analyses.Comment: The 2010 Workshop on Scheme and Functional Programmin

Introspective Pushdown Analysis of Higher-Order Programs

In the static analysis of functional programs, pushdown flow analysis and abstract garbage collection skirt just inside the boundaries of soundness and decidability. Alone, each method reduces analysis times and boosts precision by orders of magnitude. This work illuminates and conquers the theoretical challenges that stand in the way of combining the power of these techniques. The challenge in marrying these techniques is not subtle: computing the reachable control states of a pushdown system relies on limiting access during transition to the top of the stack; abstract garbage collection, on the other hand, needs full access to the entire stack to compute a root set, just as concrete collection does. \emph{Introspective} pushdown systems resolve this conflict. Introspective pushdown systems provide enough access to the stack to allow abstract garbage collection, but they remain restricted enough to compute control-state reachability, thereby enabling the sound and precise product of pushdown analysis and abstract garbage collection. Experiments reveal synergistic interplay between the techniques, and the fusion demonstrates "better-than-both-worlds" precision.Comment: Proceedings of the 17th ACM SIGPLAN International Conference on Functional Programming, 2012, AC

Automatically Deriving Spreadsheet Cell Values Using Natural Language

This disclosure describes techniques to populate spreadsheet cells that depend on, but aren’t numerically calculable from, other cells. Based on a natural language query, the empty cells of a partially populated sheet that are contextually dependent on the thus-far-filled cells are automatically filled. The techniques provide greater speed, accuracy, and scalability for datasets small and large, enabling users to efficiently explore data. The techniques obviate the need to manually populate each cell in the sheet, a time-consuming and error prone procedure that does not scale well. Automatically filling in values in a spreadsheet, as described herein, opens up possibilities for the user that don’t currently exist, e.g., answering hundreds or thousands of questions based on the context in a sheet using simple, templated, natural-language queries

Studies on bottomland hardwood forest restoration and teaching with geographic information systems (GIS) in ecology labs

The development of graduate students in the sciences preparing for careers in academia has long included elements to advance students as science researchers, but recent emphasis is being placed on developing students as instructors and education researchers as well. As such, objectives of this study included assessments of seedling responses to hydrology typical of floods in urban settings, the role of created microtopography in community development of a bottomland hardwood forest, and the influence of geographic information systems (GIS) on student motivation and conceptual knowledge. Substantial losses of bottomlands in Texas necessitate restoration to regain the ecosystem services that they provide. Restoration of proper hydrology is the most important aspect of wetland restoration, but this can prove difficult in urbanizing environments where hydrology has been irreversibly altered. Microtopography has been shown to be an important component of bottomland hardwood forests, and its restoration may aid in hydrologic restoration as gradients are created that support a diverse community. Tree seedlings were subjected to experimental flooding regimes typical of floodplain forests in rural and urban settings. Growth rates of seedlings varied over time and differed depending on species and treatment. Created microtopography resulted in a spatially heterogeneous system similar to that of natural bottomlands and strongly influenced hydrology, soil properties, survival of planted seedlings, and abundance and distribution of colonizing species. Proper bottomland restoration in urbanizing environments should include species selection based on current and potential future hydrologic conditions. In addition, restoring microtopography may improve survival of a variety of species introduced during restoration, as well as enhance colonization of a diverse plant community under changing hydrologic regimes. Trends indicated a slight improvement in attitude and performance for students that used GIS. More important, the authenticity of the experience appeared to affect student attitude. The effective use of GIS in teaching may be scale-dependent. Smallscale phenomena may be assessed as easily in a field exercise as with GIS. Using GIS to assess large-scale, complex patterns may have a substantial impact on student understanding. Further studies are needed to determine direct benefits of teaching with GIS in undergraduate ecology classrooms

Memory of the Future: Adaptive Reuse of the Seaholm Power Plant, Austin, Texas

This thesis will investigate ways in which elements and cues can be introduced to an existing building to serve the memory of the future. The project will serve as a continuation of time and space, linking what the building has been to present and future evolutions. This thesis will investigate several types of built interventions to the historic and currently unused Seaholm Power Plant site in downtown Austin, Texas, creating something greater than but inherently associated with the physical structure itself. Utilizing a concept of structures existing in different states of permanence, with different influences on memory, this project will test the ability to design into a collective memory. The attempt will be made to embellish the life and story of the Seaholm building, linking the ways it has been know before, is remembered and used now, and how it will project our heritage to those that await us

A Decomposition Approach to Multi-Vehicle Cooperative Control

We present methods that generate cooperative strategies for multi-vehicle control problems using a decomposition approach. By introducing a set of tasks to be completed by the team of vehicles and a task execution method for each vehicle, we decomposed the problem into a combinatorial component and a continuous component. The continuous component of the problem is captured by task execution, and the combinatorial component is captured by task assignment. In this paper, we present a solver for task assignment that generates near-optimal assignments quickly and can be used in real-time applications. To motivate our methods, we apply them to an adversarial game between two teams of vehicles. One team is governed by simple rules and the other by our algorithms. In our study of this game we found phase transitions, showing that the task assignment problem is most difficult to solve when the capabilities of the adversaries are comparable. Finally, we implement our algorithms in a multi-level architecture with a variable replanning rate at each level to provide feedback on a dynamically changing and uncertain environment.Comment: 36 pages, 19 figures, for associated web page see http://control.mae.cornell.edu/earl/decom