A geometric proof of the existence of definable Whitney stratifications

We give a geometric proof of existence of Whitney stratifications of definable sets in o-minimal structures.Comment: 9 pages, 1 figur

Municipal Infrastructure Delivery in Ethiopia: A bottomless pit or an option to reach the Millennium Development Goals?

The following paper examines the different options to finance local public infrastructure in Ethiopia based on the assumption that the federal government of Ethiopia will not provide any guarantees for local borrowing. Besides a detailed description of the local public finance system and the capital market in Ethiopia, the paper also sets out some international successful practices in municipal infrastructure financing. Based on the observation of the Ethiopian case and the consideration of the international experiences, the paper has two major pillars that very specifically identify actions required for implementation. On the one hand, the paper recommends a number of feasible arrangements to generate a revenue enhancement of the local authorities in the existing intergovernmental framework. On the other hand, the paper suggests a solution - for creditworthy as well as for potentially creditworthy urban local governments (ULG) - to finance their future demand of public infrastructure together with the national finance institutions as well as the international donors.Fiscal Federalism, Grants, Ethiopia, Urban and Rural Economies

Interfering directed paths and the sign phase transition

We revisit the question of the "sign phase transition" for interfering directed paths with real amplitudes in a random medium. The sign of the total amplitude of the paths to a given point may be viewed as an Ising order parameter, so we suggest that a coarse-grained theory for system is a dynamic Ising model coupled to a Kardar-Parisi-Zhang (KPZ) model. It appears that when the KPZ model is in its strong-coupling ("pinned") phase, the Ising model does not have a stable ferromagnetic phase, so there is no sign phase transition. We investigate this numerically for the case of {\ss}1+1 dimensions, demonstrating the instability of the Ising ordered phase there.Comment: 4 pages, 4 figure

Improving Lexical Choice in Neural Machine Translation

We explore two solutions to the problem of mistranslating rare words in neural machine translation. First, we argue that the standard output layer, which computes the inner product of a vector representing the context with all possible output word embeddings, rewards frequent words disproportionately, and we propose to fix the norms of both vectors to a constant value. Second, we integrate a simple lexical module which is jointly trained with the rest of the model. We evaluate our approaches on eight language pairs with data sizes ranging from 100k to 8M words, and achieve improvements of up to +4.3 BLEU, surpassing phrase-based translation in nearly all settings.Comment: Accepted at NAACL HLT 201

Soft Contract Verification

Behavioral software contracts are a widely used mechanism for governing the flow of values between components. However, run-time monitoring and enforcement of contracts imposes significant overhead and delays discovery of faulty components to run-time. To overcome these issues, we present soft contract verification, which aims to statically prove either complete or partial contract correctness of components, written in an untyped, higher-order language with first-class contracts. Our approach uses higher-order symbolic execution, leveraging contracts as a source of symbolic values including unknown behavioral values, and employs an updatable heap of contract invariants to reason about flow-sensitive facts. We prove the symbolic execution soundly approximates the dynamic semantics and that verified programs can't be blamed. The approach is able to analyze first-class contracts, recursive data structures, unknown functions, and control-flow-sensitive refinements of values, which are all idiomatic in dynamic languages. It makes effective use of an off-the-shelf solver to decide problems without heavy encodings. The approach is competitive with a wide range of existing tools---including type systems, flow analyzers, and model checkers---on their own benchmarks.Comment: ICFP '14, September 1-6, 2014, Gothenburg, Swede