ANALYSIS AND IMPLEMENTATION OF PARALLEL UNIFORM HASHING

1992 ◽  
Vol 03 (01) ◽  
pp. 55-63
Author(s):  
FABRIZIO LUCCIO ◽  
ANDREA PIETRACAPRINA ◽  
GEPPINO PUCCI
Keyword(s):  
Shared Memory ◽  
High Probability ◽  
Hash Table ◽  
Fixed Size ◽  
Hash Tables ◽  
Load Factors ◽  
Before And After

The performance of hash tables is analyzed in a parallel context. Assuming that a hash table of fixed size is allocated in the shared memory of a PRAM with n processors, a Ph-step is defined as a PRAM computation in which each processor searches or inserts a key in the table. It is shown that the maximum number of table probes needed for a single key in a Ph-step is Ω( log 1/αn) and O( log 1/α′n) with high probability, where α and α′ are the load factors before and after the execution of the Ph-step. However, a clever implementation of a Ph-step is proposed, which runs in time O(( log 1/α′n)1/2) with high probability. The algorithm exploits the fact that operations relative to different keys have different durations; hence, the processors in charge of shorter operations, once finished, are used to perform part of the longer ones.

Analysis of Robin Hood and Other Hashing Algorithms Under the Random Probing Model, With and Without Deletions

2018 ◽  
Vol 28 (4) ◽  
pp. 600-617
Author(s):  
P. V. POBLETE ◽  
A. VIOLA
Keyword(s):  
Search Algorithm ◽  
Recurrence Equation ◽  
Constant Time ◽  
Collision Resolution ◽  
Load Factor ◽  
Hash Tables ◽  
Search Cost ◽  
Robin Hood ◽  
Small Constant ◽  
Load Factors

Thirty years ago, the Robin Hood collision resolution strategy was introduced for open addressing hash tables, and a recurrence equation was found for the distribution of its search cost. Although this recurrence could not be solved analytically, it allowed for numerical computations that, remarkably, suggested that the variance of the search cost approached a value of 1.883 when the table was full. Furthermore, by using a non-standard mean-centred search algorithm, this would imply that searches could be performed in expected constant time even in a full table.In spite of the time elapsed since these observations were made, no progress has been made in proving them. In this paper we introduce a technique to work around the intractability of the recurrence equation by solving instead an associated differential equation. While this does not provide an exact solution, it is sufficiently powerful to prove a bound of π2/3 for the variance, and thus obtain a proof that the variance of Robin Hood is bounded by a small constant for load factors arbitrarily close to 1. As a corollary, this proves that the mean-centred search algorithm runs in expected constant time.We also use this technique to study the performance of Robin Hood hash tables under a long sequence of insertions and deletions, where deletions are implemented by marking elements as deleted. We prove that, in this case, the variance is bounded by 1/(1−α), where α is the load factor.To model the behaviour of these hash tables, we use a unified approach that we apply also to study the First-Come-First-Served and Last-Come-First-Served collision resolution disciplines, both with and without deletions.

scholarly journals The Maximum Displacement for Linear Probing Hashing

2013 ◽  
Vol 22 (3) ◽  
pp. 455-476
Author(s):  
NICLAS PETERSSON
Keyword(s):  
Probabilistic Model ◽  
Hash Table ◽  
Critical Value ◽  
Hash Tables ◽  
Maximum Displacement ◽  
Asymptotic Nature ◽  
Process Convergence

In this paper we study the maximum displacement for linear probing hashing. We use the standard probabilistic model together with the insertion policy known as First-Come-(First-Served). The results are of asymptotic nature and focus on dense hash tables. That is, the number of occupied cellsnand the size of the hash tablemtend to infinity with ration/m→ 1. We present distributions and moments for the size of the maximum displacement, as well as for the number of items with displacement larger than some critical value. This is done via process convergence of the (appropriately normalized) length of the largest block of consecutive occupied cells, when the total number of occupied cellsnvaries.

Template Calibration Parameter Optimization of Fuzzy Vault Method

2019 ◽  
Vol 34 (07) ◽  
pp. 2059020
Author(s):  
Yifan Liao
Keyword(s):  
Hash Table ◽  
Rejection Rate ◽  
Base Point ◽  
Matching Accuracy ◽  
Fuzzy Vault ◽  
Fuzzy Point ◽  
Before And After ◽  
Common Technique ◽  
Point Distance ◽  
Fingerprint Database

In the concrete implementation of the fuzzy vault algorithm, the geometric hash method is a common technique for automatic calibration of biometric templates. For the fuzzy problem of parameter acquisition, the matching accuracy of fuzzy vault template is affected in the three parameters: the pixel size, hash table and hash table quantization parameters ([Formula: see text] and [Formula: see text]). The single factor experiment method obtains the optimal range of these three parameters, and the extraction range of the fuzzy point and the selection rule of the base point distance are improved for the fuzzy vault algorithm. Finally, based on the FVC fingerprint database, their matching precision is compared for the algorithm before and after optimization. The experimental results show that the false rejection rate (FRR) of the optimized algorithm is reduced by at least 9.84%, and the false acceptance rate (FAR) is reduced by at least 7.12%, indicating that the optimization scheme improves the matching accuracy of the algorithm. The algorithm has certain robustness and practicability.

scholarly journals HD-Tree: An Efficient High-Dimensional Virtual Index Structure Using a Half Decomposition Strategy

Algorithms ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 338
Author(s):  
Ting Huang ◽  
Zhengping Weng ◽  
Gang Liu ◽  
Zhenwen He
Keyword(s):  
Hash Table ◽  
Index Structure ◽  
High Dimensional ◽  
Sequential Search ◽  
Storage Space ◽  
Hash Tables ◽  
Time Performance ◽  
Indexing Method ◽  
Point Data ◽  
Better Than

To manage multidimensional point data more efficiently, this paper presents an improvement, called HD-tree, of a previous indexing method, called D-tree. Both structures combine quadtree-like partitioning (using integer shift operations without storing internal nodes, but only leaves) and hash tables (for searching for the nodes stored). However, the HD-tree follows a brand-new decomposition strategy, which is called half decomposition strategy. This improvement avoids the generation of nodes containing only a small amount of data and the sequential search of the hash table, so that it can save storage space while having faster I/O and better time performance when building the tree and querying data. The results demonstrate convincingly that the time and space performance of HD-tree is better than that of D-tree regardless of uniform or uneven data, which are less affected by data distribution.

scholarly journals Compact and hash based variants of the suffix array

2017 ◽  
Vol 65 (4) ◽  
pp. 407-418
Author(s):  
S. Grabowski ◽  
M. Raniszewski
Keyword(s):  
Data Structure ◽  
Full Text ◽  
Hash Table ◽  
Suffix Array ◽  
Fixed Size ◽  
Text Indexing ◽  
Text Length ◽  
Speed Up ◽  
Pattern Searches ◽  
Search Interval

AbstractFull-text indexing aims at building a data structure over a given text capable of efficiently finding arbitrary text patterns, and possibly requiring little space. We propose two suffix array inspired full-text indexes. One, called SA-hash, augments the suffix array with a hash table to speed up pattern searches due to significantly narrowed search interval before the binary search phase. The other, called FBCSA, is a compact data structure, similar to Mäkinen’s compact suffix array (MakCSA), but working on fixed size blocks. Experiments on the widely used Pizza & Chili datasets show that SA-hash is about 2–3 times faster in pattern searches (counts) than the standard suffix array, for the price of requiring 0.2n–1.1nbytes of extra space, wherenis the text length. FBCSA, in one of the presented variants, reduces the suffix array size by a factor of about 1.5–2, while it gets close in search times, winning in speed with its competitors known from the literature, MakCSA and LCSA.

scholarly journals Application of Vibroacoustic Diagnosis in Assessing Bridges Connecting Teeth and Implants to Treat Tooth Absence in Sea Vessel Crews

2020 ◽  
Vol 27 (1) ◽  
pp. 188-194
Author(s):  
Artur Rasinski ◽  
Grzegorz Klekot ◽  
Piotr Skopiński
Keyword(s):  
High Probability ◽  
Small Extent ◽  
Missing Teeth ◽  
Pilot Studies ◽  
Before And After ◽  
Acoustic Techniques ◽  
Natural Teeth ◽  
Mutual Relations ◽  
Proven Method ◽  
Implant Treatment

AbstractImplant treatment is a proven method in dentistry for partial and complete missing teeth reconstruction. In some clinical situations it is advisable to limit the number of implants, which can be obtained by making a bridge connecting the patient’s own tooth with the implant. So far, the possibility of using safe and permanent connections of natural teeth with implants has been examined to a small extent due to the dangers resulting from the different mobility of dental implants and teeth.An attempt was made to use vibro-acoustic techniques to evaluate various combinations of teeth and implants. Pilot studies were carried out on cadavers-pig mandibles with implants. There were recorded sounds in the immediate vicinity of the mandible formed in response to impulse excitations carried out with a point hit against a tooth or implant before and after their joining with a bridge. The comparison of spectra allows to see features indicating a high probability of being able to distinguish between the examined configurations.The results of the research should contribute to a better understanding of the mutual relations between the dental implant and the tooth, which are included in bridge. In the perspective, it will enable to assess the level of safety and to identify clinical situations that allow to obtain dental bridges based on teeth and implants.

Modeling of the Pohang Earthquake Probability Using the Seismogenic Index

2020 ◽  
Author(s):  
Serge Shapiro ◽  
Jin-Han Ree
Keyword(s):  
High Probability ◽  
Temporal Evolution ◽  
B Value ◽  
Observation System ◽  
Geothermal System ◽  
Earthquake Probability ◽  
Index Model ◽  
Before And After ◽  
Event Location ◽  
Homogeneous Porous Medium

<p>A strong earthquake of Mw5.5 occurred on 15 November 2017, shortly after finishing borehole fluid injections performed for the geothermal development of the Pohang Enhanced Geothermal System. With a high probability, the earthquake was triggered by these operations. In this work we consider the Pohang Earthquake in the frame of the Seismogenic Index Model. We attempt to estimate the triggering probability of this event as well as a general  probability of triggering of arbitrary-magnitude earthquakes at the Pohang site before and after the termination of the fluid injections. A fluid injection in a point of an infinite continuum is taken here as a prototype of the Pohang situation.</p><p>The seismogenic index of the Pohang site is approximately between -2 and -1. During the injection operations, one can observe  a tendency of the<br>seismogenic index to increase with time. This was possibly  an indication of a gradual involvement of seismically more active zones in the stimulated domain. Especially alarming was the event of Mw3.3 on April 15th of 2017. Probably, this event indicated a jump of the seismogenic index to -1. All injection operations in both boreholes should be stopped after this event.</p><p>Our estimate of the probability of the Pohang earthquake is approximately 15%. One of  decisive factors for  this relatively high probability was the low b value. A combination of a low b-value and a rather high seismogenic index made the probability of a hazardous event significant. A termination of all injection operations after the occurrence of the event of M_w3.3 would significantly reduce the probability of an M_w5.5 event down to approximately 3%. An injection termination at M_w2.3 would reduce it down to approximately 1%.</p><p>The Pohang earthquake has a clear character of a triggered event. A real-time well developed seismic observation system permitting a precise 3-D event location and a monitoring of the temporal evolution of the geometry of the stimulated volume and of the seismogenic index could potentially help to prevent or to delay the occurrence of such an  earthquake.</p><p>This paper provides a simplified consideration based on analytical formulations for an effective homogeneous porous medium and monotonic injection operations. Numerical simulations of more realistic injection configurations,  an analysis of modeling results along the indicated here directions, further enhanced processing and analysis of seismologic records are required for more detailed understanding of processes led to the Pohang event. </p>

First and second meal effects of pulses on blood glucose, appetite, and food intake at a later meal

2011 ◽  
Vol 36 (5) ◽  
pp. 634-642 ◽  
Author(s):  
Rebecca C. Mollard ◽  
Christina L. Wong ◽  
Bohdan L. Luhovyy ◽  
G. Harvey Anderson
Keyword(s):  
Blood Glucose ◽  
Food Intake ◽  
Test Meal ◽  
Fixed Size ◽  
Tomato Sauce ◽  
Beneficial Effects ◽  
Before And After ◽  
Pulse Type ◽  
Effect Of Treatment ◽  
Ad Libitum

Pulses are low-glycemic appetite-suppressing foods, but it is not known whether these properties persist after being consumed as part of a meal and after a second meal. The objective of this study was to determine the effects of a fixed-size pulse meal on appetite and blood glucose (BG) before and after an ad libitum test meal (pizza) and on food intake (FI) at the test meal. Males (n = 25; 21.3 ± 0.5 years; 21.6 ± 0.3 kg·m–2) randomly consumed 4 isocaloric meals: chickpea; lentil; yellow split pea; and macaroni and cheese (control). Commercially available canned pulses provided 250 kcal, and were consumed with macaroni and tomato sauce. FI was measured at a pizza meal 260 min after consumption of the isocaloric meal. BG and appetite were measured from 0 to 340 min. The lentil and yellow pea, but not chickpea, treatments led to lower appetite ratings during the 260 min prepizza meal period, and less FI at the pizza meal, compared with macaroni and cheese (p < 0.05). All pulse treatments lowered BG immediately following consumption (at 20 min) (p < 0.05), but there was no effect of treatment on prepizza meal BG AUC (p = 0.07). Immediately after the pizza meal, BG was lower following the chickpea and lentil treatments, but not the yellow pea treatment (p < 0.05). Postpizza meal BG AUC was lower following the chickpea and lentil treatments than in the yellow pea treatment (p < 0.05). The beneficial effects of consuming a pulse meal on appetite, FI at a later meal, and the BG response to a later meal are dependent on pulse type.

A SCALABLE AND EFFICIENT STORAGE ALLOCATOR ON SHARED-MEMORY MULTIPROCESSORS

2001 ◽  
Vol 11 (02n03) ◽  
pp. 313-325
Author(s):  
VOON-YEE VEE ◽  
WEN-JING HSU
Keyword(s):  
Shared Memory ◽  
Parallel Simulation ◽  
Parallel Programs ◽  
Fixed Size ◽  
Shared Memory Multiprocessors ◽  
Efficient Storage ◽  
Dynamic Storage ◽  
Time Critical ◽  
Lock Contention

An efficient dynamic storage allocator is important for time-critical parallel programs. In this paper, we present a fast and simple parallel allocator for fixed size blocks on shared-memory multiprocessors. We show both theoretically and empirically that the allocator incurs very low lock contention. The allocator is tested with parallel simulation applications with frequent allocation and release requests. The results confirm that our allocator is indeed very efficient.

FMPC: A Fast Multi-Dimensional Packet Classification Algorithm

2014 ◽  
Vol 644-650 ◽  
pp. 3365-3370
Author(s):  
Zhen Hong Guo ◽  
Lin Li ◽  
Qing Wang ◽  
Meng Lin ◽  
Rui Pan
Keyword(s):  
Rapid Development ◽  
Hash Table ◽  
Bloom Filter ◽  
Packet Classification ◽  
Binary Search ◽  
Bloom Filters ◽  
Algorithm Analysis ◽  
Hash Tables ◽  
Worst Case ◽  
Embedded Sram

With the rapid development of the Internet, the number of firewall rules is increasing. The enormous quantity of rules challenges the performance of the packet classification that has already become a bottleneck in firewalls. This dissertation proposes a rapid and multi-dimensional algorithm for packet classification based on BSOL(Binary Search On Leaves), which is named FMPC(FastMulti-dimensional Packet Classification). Different from BSOL, FMPC cuts all dimensions at the same time to decompose rule spaces and stores leaf spaces into hash tables; FMPC constructs a Bloom Filter for every hash table and stores them into embedded SRAM. When classifying a packet, FMPC performs parallel queries on Bloom Filters and determines how to visit hash tables according to the results. Algorithm analysis and the result of simulations show: the average number of hash-table lookups of FMPC is 1 when classifying a packet, which is much smaller than that of BSOL; inthe worst case, the number of hash-table lookups of FMPCisO(logwmax+1⁡), which is also smaller than that of BSOL in multi-dimensional environment, where wmax is the length, in bits, of the dimension whose length is the longest..

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