PotLLL: A Polynomial Time Version of LLL With Deep Insertions

Lattice reduction algorithms have numerous applications in number theory, algebra, as well as in cryptanalysis. The most famous algorithm for lattice reduction is the LLL algorithm. In polynomial time it computes a reduced basis with provable output quality. One early improvement of the LLL algorithm was LLL with deep insertions (DeepLLL). The output of this version of LLL has higher quality in practice but the running time seems to explode. Weaker variants of DeepLLL, where the insertions are restricted to blocks, behave nicely in practice concerning the running time. However no proof of polynomial running time is known. In this paper PotLLL, a new variant of DeepLLL with provably polynomial running time, is presented. We compare the practical behavior of the new algorithm to classical LLL, BKZ as well as blockwise variants of DeepLLL regarding both the output quality and running time.Comment: 17 pages, 8 figures; extended version of arXiv:1212.5100 [cs.CR

Solving the LPN problem in cube-root time

In this paper it is shown that given a sufficient number of (noisy) random binary linear equations, the Learning from Parity with Noise (LPN) problem can be solved in essentially cube root time in the number of unknowns. The techniques used to recover the solution are known from fast correlation attacks on stream ciphers. As in fast correlation attacks, the performance of the algorithm depends on the number of equations given. It is shown that if this number exceeds a certain bound, and the bias of the noisy equations is polynomial in number of unknowns, the running time of the algorithm is reduced to almost cube root time compared to the brute force checking of all possible solutions. The mentioned bound is explicitly given and it is further shown that when this bound is exceeded, the complexity of the approach can even be further reduced

A nation-wide laboratory: Examining trust and trustworthiness by integrating behavioral experiments into representative surveys

Typically, laboratory experiments suffer from homogeneous subject pools and selfselection biases. The usefulness of survey data is limited by measurement error and by the questionability of their behavioral relevance. Here we present a method integrating interactive experiments and representative surveys thereby overcoming crucial weaknesses of both approaches. One of the major advantages of our approach is that it allows for the integration of experiments, which require interaction among the participants, with a survey of non-interacting respondents in a smooth and inexpensive way. We illustrate the power of our approach with the analysis of trust and trustworthiness in Germany by combining representative survey data with representative behavioral data from a social dilemma experiment. We identify which survey questions intended to elicit peoples trust correlate well with behaviorally exhibited trust in the experiment. People above the age of 65, highly skilled workers and people living in bigger households exhibit less trusting behavior. Foreign citizens, Catholics and people favoring the Social Democratic Party or the Christian Democratic Party exhibit more trust. People above the age of 65 and those in good health behave more trustworthy or more altruistically, respectively. People below the age of 35, the unemployed and people who say they are in favor of none of the political parties behave less trustworthy or less altruistically, respectively. -- Die experimentelle Ökonomie führt typischerweise Labor-Untersuchungen durch, die mit homogenen und selektiven Versuchspersonen arbeiten. Repräsentative Surveys leiden hingegen unter Meßfehlern und der Frage, ob hypothetisches Verhalten, das erhoben wird, mit tatsächlichem Verhalten korrespondiert. Deswegen präsentieren wir eine Methode, mit der man die Schwächen beider Ansätze überwindet, indem man Survey-Daten mit Experimenten kombiniert. Die von uns entwickelte Methode hat den Vorzug, dass sie es auf preiswerte Art und Weise erlaubt, Experimente, die die Interaktion zweier Personen erfordern, mit Standard-Surveys zu kombinieren, die auf der Unabhängigkeit der befragten Personen beruhen. Wir illustrieren die Möglichkeiten unserer Methodik mit einer Untersuchung über Vertrauen und Vertrauenswürdigkeit in Deutschland, bei der eine repräsentative Umfrage mit einem Experiment über eine Dilemma-Situation verbunden wurde. Unsere Resultate zeigen zum einen, dass nicht alle Survey-Fragen über Vertrauen mit den Ergebnissen des Experiments korrelieren. Zum zweiten zeigen unsere Ergebnisse, dass ältere Menschen (65 Jahre und älter), Hochqualifizierte und Personen, die in grösseren Haushalten leben, im Experiment unterdurchschnittlich Vertrauen offenbaren. Für Ausländer, Katholiken und die Anhänger der großen Volksparteien finden wir überdurchschnittliches Vertrauen. Vertrauenswürdigkeit bzw. Altruismus zeigen im Experiment Ältere und Befragte mit gutem Gesundheitszustand. Unterdurchschnittliche Vertrauenswüdigkeit bzw. Altruismus zeigen jüngere Befragte (bis zu 35 Jahren), arbeitslos Gemeldete und Befragte ohne eine Parteineigung.Experiment,Survey,Trust,Trustworthiness,Altruism

On the Construction of Common Size, Value and Momentum Factors in International Stock Markets: A Guide with Applications

Demand is growing for a better understanding of how assets are priced in countries outside of the U.S. While financial data are available for many firms world-wide, it is important to have a reliable and replicable method of constructing high-quality systematic risk factors from these data. This paper first documents that appropriately screened data from Thomson Reuters Datastream and Thomson Reuters Worldscope can be used to replicate closely not only U.S. market returns and the corresponding momentum risk factor (as existing work has suggested), but also the widely-used U.S. size and value risk factors. We then build novel pan-European and country-specific momentum, size, and value risk factors. By comparing our pan-European market returns and risk factors with their counterparts in the U.S., we find that they are astonishingly highly correlated. The factors we compute are made available to other researchers.Risk factors; value, size, momentum, international equity markets, asset pricing anomalies

Comparison of different lattice definitions of the topological charge

We present a comparison of different definitions of the topological charge on the lattice, using a small-volume ensemble with 2 flavours of dynamical twisted mass fermions. The investigated definitions are: index of the overlap Dirac operator, spectral projectors, spectral flow of the Hermitian Wilson-Dirac operator and field theoretic with different kinds of smoothing of gauge fields (HYP and APE smearings, gradient flow, cooling). We also show some results on the topological susceptibility.Comment: 7 pages, 2 figures, presented at the 32nd International Symposium on Lattice Field Theory (Lattice 2014), 23-28 June 2014, Columbia University, New York, NY, US

Which Swiss Gnomes Attract Money? Efficiency and Reputation as Performance Drivers of Wealth Management Banks

Wealth management constitutes an important aspect of today's banking world, but very little is known about what explains the differences among banks in their ability to attract new assets under management. Using a unique panel database of Swiss private banks, we test the hypothesis that the performance of a bank in attracting new money depends on two input factors: skill and reputation. Relatively skilled banks -- that is, banks that are more cost-efficient than predicted by their input factors -- also perform better in attracting net new money. We also find that negative media coverage (such as in the context of fraudulent business practices related to tax evasion) strongly diminishes the future ability to attract assets under management, especially at small banks. The present value of lost profits is 3.35 (0.73) times the median annual net profit of a small (large) bank. Thus, adding to the explicit fines that many Swiss banks had to pay in the course of the U.S. Department of Justice's investigations, there are substantial implicit and reputational costs to banks of having negative media coverage. Investment performance for clients seems not to explain future net new money growth. In sum, these results underscore the importance of trust in money management