Recursive n-gram hashing is pairwise independent, at best

Many applications use sequences of n consecutive symbols (n-grams). Hashing these n-grams can be a performance bottleneck. For more speed, recursive hash families compute hash values by updating previous values. We prove that recursive hash families cannot be more than pairwise independent. While hashing by irreducible polynomials is pairwise independent, our implementations either run in time O(n) or use an exponential amount of memory. As a more scalable alternative, we make hashing by cyclic polynomials pairwise independent by ignoring n-1 bits. Experimentally, we show that hashing by cyclic polynomials is is twice as fast as hashing by irreducible polynomials. We also show that randomized Karp-Rabin hash families are not pairwise independent.Comment: See software at https://github.com/lemire/rollinghashcp

Neural Processing of Short-Term Recurrence in Songbird Vocal Communication

BACKGROUND: Many situations involving animal communication are dominated by recurring, stereotyped signals. How do receivers optimally distinguish between frequently recurring signals and novel ones? Cortical auditory systems are known to be pre-attentively sensitive to short-term delivery statistics of artificial stimuli, but it is unknown if this phenomenon extends to the level of behaviorally relevant delivery patterns, such as those used during communication. METHODOLOGY/PRINCIPAL FINDINGS: We recorded and analyzed complete auditory scenes of spontaneously communicating zebra finch (Taeniopygia guttata) pairs over a week-long period, and show that they can produce tens of thousands of short-range contact calls per day. Individual calls recur at time scales (median interval 1.5 s) matching those at which mammalian sensory systems are sensitive to recent stimulus history. Next, we presented to anesthetized birds sequences of frequently recurring calls interspersed with rare ones, and recorded, in parallel, action and local field potential responses in the medio-caudal auditory forebrain at 32 unique sites. Variation in call recurrence rate over natural ranges leads to widespread and significant modulation in strength of neural responses. Such modulation is highly call-specific in secondary auditory areas, but not in the main thalamo-recipient, primary auditory area. CONCLUSIONS/SIGNIFICANCE: Our results support the hypothesis that pre-attentive neural sensitivity to short-term stimulus recurrence is involved in the analysis of auditory scenes at the level of delivery patterns of meaningful sounds. This may enable birds to efficiently and automatically distinguish frequently recurring vocalizations from other events in their auditory scene

Anerkjennelse – forskjellen som gjør en forskjell. En empirisk studie av fenomenet anerkjennelse i et ledelsesperspektiv

Hensikten med denne masteroppgaven er å sette lys på betydningen av fenomenet anerkjennelse i et ledelsesperspektiv

Visualizing and Modeling Categorical Time Series Data

Categorical time series data can not be effectively visualized and modeled using methods developed for ordinary data. The arbitrary mapping of categorical data to ordinal values can have a number of undesirable consequences. New techniques for visualizing and modeling categorical time series data are described, and examples are presented using computer and communications network traces

Two Performance Tool Design Issues and CHITRA's Solutions

Two issues arising in the design of trace-file based performance analysis tools are discussed: handling categorical rather than just numeric data and correctly inferring system behavior from trace data by using not one but multiple trace files. The issues are illustrated using the problem of determining whether damaging oscillations occur in the all points shortest path algorithm when used for routing messages between processors. Solutions used by the Chitra trace analysis tool are discussed