Rating Shopping and Rating Inflation: Empirical Evidence from Israel

The collapse of structured bond ratings during the 2007-2008 financial crisis called attention to the possibility of rating inflation due to lowered rating standards and rating shopping. Nevertheless, little empirical evidence has been offered for this prospect. The Israeli corporate credit rating market serves as solid ground for investigating this matter. In this study, we use data on corporate bond ratings assigned by two local rating agencies affiliated with S&P and Moody’s during the period 2004-2009. We show that while one agency (Midroog) systematically assigned higher ratings, the ratings of the other agency (S&P-Maalot) were inflated due to rating shopping. These conclusions are based on several findings: the presence of selection bias in dual ratings, the superior accounting features of firms rated by S&P-Maalot relative to those similarly rated by Midroog, and the greater tendency of single ratings by S&P-Maalot to be downgraded. We confirm the predictions of recent theoretical studies that rating inflation may occur even when the value of the rating agencies derives from their reputation.

Efficient Algorithms for Finding Maximal Matching in Graphs

This paper surveys the techniques used for designing the most efficient algorithms for finding a maximum cardinality or weighted matching in (general or bipartite) graphs. It also lists some open problems concerning possible improvements in existing algorithms and the existence of fast parallel algorithms for these problems

Desalination effluents and the establishment of the non-indigenous skeleton shrimp Paracaprella pusilla Mayer, 1890 in the south-eastern Mediterranean

A decade long monitoring programme has revealed a flourishing population of the non-indigenous skeleton shrimp Paracaprella pusilla in the vicinity of outfalls of desalination plants off the Mediterranean coast of Israel. The first specimens were collected in 2010, thus predating all previously published records of this species in the Mediterranean Sea. A decade-long disturbance regime related to the construction and operation of the plants may have had a critical role in driving the population growth

Desalination effluents and the establishment of the non-indigenous skeleton shrimp Paracaprella pusilla Mayer, 1890 in the south-eastern Mediterranean

A decade long monitoring programme has revealed a flourishing population of the non-indigenous skeleton shrimp Paracaprella pusilla in the vicinity of outfalls of desalination plants off the Mediterranean coast of Israel. The first specimens were collected in 2010, thus predating all previously published records of this species in the Mediterranean Sea. A decade-long disturbance regime related to the construction and operation of the plants may have had a critical role in driving the population growth

Data structures and algorithms for approximate string matching Zvi Galil, Raffaele Giancarlo

This paper surveys techniques for designing efficient sequential and parallel approximate string matching algorithms. Special attention is given to the methods for the construction of data structures that efficiently support primitive operations needed in approximate string matching

An Improved Algorithm for Approximate String Matching

Given a text string, a pattern string, and an integer k, a new algorithm for finding all occurrences of the pattern string in the text string with at most k differences is presented. Both its theoretical and practical variants improve the known algorithms

Two Lower Bounds In Asynchronous Distributed Computation

We introduce new techniques for deriving lower bounds on the message complexity in asynchronous distributed computation. These techniques combine the choice of specific patterns of communication delays and crossing sequence arguments with consideration of the speed of propagation of messages, together with careful counting of messages in different parts of the network. They enable us to prove the following results, settling two open problems: An Ω(n log* n) lower bound for the number of messages sent by an asynchronous algorithm for computing any nonconstant function on a bidirectional ring of n anonymous processors. An Ω(n log n) lower bound for the average number of messages sent by any maximum finding algorithm on a ring of n processors, in case n is known

Speeding up dynamic programming with applications to molecular biology

Consider the problem of computing E[j] = mit:! {D[k] + w(k, j)}, j = 1, ... , n, O~k~]-l where w is a given weight function, D[D] is given and for every k = 1, ... , n, D[k] is easily computable from E[k]. This problem appears as a subproblem in dynamic programming solutions to various problems. Obviously, it can be solved in time O( n2 ), and for a general weight function no better algorithm is possible. We consider two dual cases that arise in applications: In the concave case, the weight function satisfies the quadrangle inequality: w(k,j) + w(l,j') ~ w(l,j) +w(k,j'), for all k ~ 1 ~ j ~ j'. In the convex case, the weight function satisfies the inverse quadrangle inequality. In both cases we show how to use the assumed property of w to derive an O( n log n) algorithm. Even better, linear-time algorithms are obtained if w satisfies the following additional closest zero property: for every two integers 1 and k, 1 < k, and real number a, the smallest zero of f(x) = w(l,x) - w(k,x) - a which is larger than 1 can be found in constant time. Surprisingly, the two algorithms are also dual in the following sense: Both work in stages. In the j-th stage they compute Elj]. They maintain a set of candidates which satisfies the property that Elj] depends only on D[k] + w(k, j) for k's in the set. Moreover, each algorithm discards candidates from the set, and discarded candidates never rejoin the set. To be able to maintain such a set of candidates efficiently one uses the following "dual" data structures: a queue in the concave case and a stack in the convex case. The two algorithms speed up several dynamic programming routines that solve as a subproblem the problem above. The speed-up is from O(n3 ) to O(n2Iogn) or O(n2 ). Applications include algorithms for comparing DNA sequences, algorithms for determining the secondary structure of RNA, and algorithms used in speech recognition and geology. One typical problem is the following: Given the cost of substituting any pair of symbols and a convex cost function g for gaps (where g(r) is the cost of a gap of size r), compute the modified edit distance between the two given sequences