121 research outputs found
Higher-Order Triangular-Distance Delaunay Graphs: Graph-Theoretical Properties
We consider an extension of the triangular-distance Delaunay graphs
(TD-Delaunay) on a set of points in the plane. In TD-Delaunay, the convex
distance is defined by a fixed-oriented equilateral triangle ,
and there is an edge between two points in if and only if there is an empty
homothet of having the two points on its boundary. We consider
higher-order triangular-distance Delaunay graphs, namely -TD, which contains
an edge between two points if the interior of the homothet of
having the two points on its boundary contains at most points of . We
consider the connectivity, Hamiltonicity and perfect-matching admissibility of
-TD. Finally we consider the problem of blocking the edges of -TD.Comment: 20 page
Ninth and Tenth Order Virial Coefficients for Hard Spheres in D Dimensions
We evaluate the virial coefficients B_k for k<=10 for hard spheres in
dimensions D=2,...,8. Virial coefficients with k even are found to be negative
when D>=5. This provides strong evidence that the leading singularity for the
virial series lies away from the positive real axis when D>=5. Further analysis
provides evidence that negative virial coefficients will be seen for some k>10
for D=4, and there is a distinct possibility that negative virial coefficients
will also eventually occur for D=3.Comment: 33 pages, 12 figure
Algorithms for Power Aware Testing of Nanometer Digital ICs
At-speed testing of deep-submicron digital very large scale integrated (VLSI) circuits
has become mandatory to catch small delay defects. Now, due to continuous shrinking
of complementary metal oxide semiconductor (CMOS) transistor feature size, power
density grows geometrically with technology scaling. Additionally, power dissipation
inside a digital circuit during the testing phase (for test vectors under all fault models
(Potluri, 2015)) is several times higher than its power dissipation during the normal
functional phase of operation. Due to this, the currents that flow in the power grid during
the testing phase, are much higher than what the power grid is designed for (the
functional phase of operation). As a result, during at-speed testing, the supply grid
experiences unacceptable supply IR-drop, ultimately leading to delay failures during
at-speed testing. Since these failures are specific to testing and do not occur during
functional phase of operation of the chip, these failures are usually referred to false
failures, and they reduce the yield of the chip, which is undesirable.
In nanometer regime, process parameter variations has become a major problem.
Due to the variation in signalling delays caused by these variations, it is important to
perform at-speed testing even for stuck faults, to reduce the test escapes (McCluskey
and Tseng, 2000; Vorisek et al., 2004). In this context, the problem of excessive peak
power dissipation causing false failures, that was addressed previously in the context of
at-speed transition fault testing (Saxena et al., 2003; Devanathan et al., 2007a,b,c), also
becomes prominent in the context of at-speed testing of stuck faults (Maxwell et al.,
1996; McCluskey and Tseng, 2000; Vorisek et al., 2004; Prabhu and Abraham, 2012;
Potluri, 2015; Potluri et al., 2015). It is well known that excessive supply IR-drop during
at-speed testing can be kept under control by minimizing switching activity during
testing (Saxena et al., 2003). There is a rich collection of techniques proposed in the past
for reduction of peak switching activity during at-speed testing of transition/delay faults
ii
in both combinational and sequential circuits. As far as at-speed testing of stuck faults
are concerned, while there were some techniques proposed in the past for combinational
circuits (Girard et al., 1998; Dabholkar et al., 1998), there are no techniques concerning
the same for sequential circuits. This thesis addresses this open problem. We
propose algorithms for minimization of peak switching activity during at-speed testing
of stuck faults in sequential digital circuits under the combinational state preservation
scan (CSP-scan) architecture (Potluri, 2015; Potluri et al., 2015). First, we show that,
under this CSP-scan architecture, when the test set is completely specified, the peak
switching activity during testing can be minimized by solving the Bottleneck Traveling
Salesman Problem (BTSP). This mapping of peak test switching activity minimization
problem to BTSP is novel, and proposed for the first time in the literature.
Usually, as circuit size increases, the percentage of don’t cares in the test set increases.
As a result, test vector ordering for any arbitrary filling of don’t care bits
is insufficient for producing effective reduction in switching activity during testing of
large circuits. Since don’t cares dominate the test sets for larger circuits, don’t care
filling plays a crucial role in reducing switching activity during testing. Taking this
into consideration, we propose an algorithm, XStat, which is capable of performing test
vector ordering while preserving don’t care bits in the test vectors, following which, the
don’t cares are filled in an intelligent fashion for minimizing input switching activity,
which effectively minimizes switching activity inside the circuit (Girard et al., 1998).
Through empirical validation on benchmark circuits, we show that XStat minimizes
peak switching activity significantly, during testing.
Although XStat is a very powerful heuristic for minimizing peak input-switchingactivity,
it will not guarantee optimality. To address this issue, we propose an algorithm
that uses Dynamic Programming to calculate the lower bound for a given sequence
of test vectors, and subsequently uses a greedy strategy for filling don’t cares in this
sequence to achieve this lower bound, thereby guaranteeing optimality. This algorithm,
which we refer to as DP-fill in this thesis, provides the globally optimal solution for
minimizing peak input-switching-activity and also is the best known in the literature
for minimizing peak input-switching-activity during testing. The proof of optimality of
DP-fill in minimizing peak input-switching-activity is also provided in this thesis
Connectivity Oracles for Graphs Subject to Vertex Failures
We introduce new data structures for answering connectivity queries in graphs
subject to batched vertex failures. A deterministic structure processes a batch
of failed vertices in time and thereafter
answers connectivity queries in time. It occupies space . We develop a randomized Monte Carlo version of our data structure
with update time , query time , and space
for any failure bound . This is the first connectivity oracle for
general graphs that can efficiently deal with an unbounded number of vertex
failures.
We also develop a more efficient Monte Carlo edge-failure connectivity
oracle. Using space , edge failures are processed in time and thereafter, connectivity queries are answered in
time, which are correct w.h.p.
Our data structures are based on a new decomposition theorem for an
undirected graph , which is of independent interest. It states that
for any terminal set we can remove a set of
vertices such that the remaining graph contains a Steiner forest for with
maximum degree
Improved Algorithms for the Steiner Problem in Networks
We present several new techniques for dealing with the Steiner problem in (undirected) networks. We consider them as building blocks of an exact algorithm, but each of them could also be of interest in its own right. First, we consider some relaxations of integer programming formulations of this problem and investigate different methods for dealing with these relaxations, not only to obtain lower bounds, but also to get additional information which is used in the computation of upper bounds and in reduction techniques. Then, we modify some known reduction tests and introduce some new ones. We integrate some of these tests into a package with a small worst case time which achieves impressive reductions on a wide range of instances. On the side of upper bounds, we introduce the new concept of heuristic reductions. On the basis of this concept, we develop heuristics that achieve sharper upper bounds than the strongest known heuristics for this problem despite running times which are smaller by orders of magnitude. Finally, we integrate these blocks into an exact algorithm. We present computational results on a variety of benchmark instances. The results are clearly superior to those of all other exact algorithms known to the authors
Theoretically Efficient Parallel Graph Algorithms Can Be Fast and Scalable
There has been significant recent interest in parallel graph processing due
to the need to quickly analyze the large graphs available today. Many graph
codes have been designed for distributed memory or external memory. However,
today even the largest publicly-available real-world graph (the Hyperlink Web
graph with over 3.5 billion vertices and 128 billion edges) can fit in the
memory of a single commodity multicore server. Nevertheless, most experimental
work in the literature report results on much smaller graphs, and the ones for
the Hyperlink graph use distributed or external memory. Therefore, it is
natural to ask whether we can efficiently solve a broad class of graph problems
on this graph in memory.
This paper shows that theoretically-efficient parallel graph algorithms can
scale to the largest publicly-available graphs using a single machine with a
terabyte of RAM, processing them in minutes. We give implementations of
theoretically-efficient parallel algorithms for 20 important graph problems. We
also present the optimizations and techniques that we used in our
implementations, which were crucial in enabling us to process these large
graphs quickly. We show that the running times of our implementations
outperform existing state-of-the-art implementations on the largest real-world
graphs. For many of the problems that we consider, this is the first time they
have been solved on graphs at this scale. We have made the implementations
developed in this work publicly-available as the Graph-Based Benchmark Suite
(GBBS).Comment: This is the full version of the paper appearing in the ACM Symposium
on Parallelism in Algorithms and Architectures (SPAA), 201
Log Diameter Rounds Algorithms for 2-Vertex and 2-Edge Connectivity
Many modern parallel systems, such as MapReduce, Hadoop and Spark, can be modeled well by the MPC model. The MPC model captures well coarse-grained computation on large data - data is distributed to processors, each of which has a sublinear (in the input data) amount of memory and we alternate between rounds of computation and rounds of communication, where each machine can communicate an amount of data as large as the size of its memory. This model is stronger than the classical PRAM model, and it is an intriguing question to design algorithms whose running time is smaller than in the PRAM model.
In this paper, we study two fundamental problems, 2-edge connectivity and 2-vertex connectivity (biconnectivity). PRAM algorithms which run in O(log n) time have been known for many years. We give algorithms using roughly log diameter rounds in the MPC model. Our main results are, for an n-vertex, m-edge graph of diameter D and bi-diameter D\u27, 1) a O(log D log log_{m/n} n) parallel time 2-edge connectivity algorithm, 2) a O(log D log^2 log_{m/n}n+log D\u27log log_{m/n}n) parallel time biconnectivity algorithm, where the bi-diameter D\u27 is the largest cycle length over all the vertex pairs in the same biconnected component. Our results are fully scalable, meaning that the memory per processor can be O(n^{delta}) for arbitrary constant delta>0, and the total memory used is linear in the problem size. Our 2-edge connectivity algorithm achieves the same parallel time as the connectivity algorithm of [Andoni et al., 2018]. We also show an Omega(log D\u27) conditional lower bound for the biconnectivity problem
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