New Classes of Partial Geometries and Their Associated LDPC Codes

The use of partial geometries to construct parity-check matrices for LDPC codes has resulted in the design of successful codes with a probability of error close to the Shannon capacity at bit error rates down to $10^{-15}$. Such considerations have motivated this further investigation. A new and simple construction of a type of partial geometries with quasi-cyclic structure is given and their properties are investigated. The trapping sets of the partial geometry codes were considered previously using the geometric aspects of the underlying structure to derive information on the size of allowable trapping sets. This topic is further considered here. Finally, there is a natural relationship between partial geometries and strongly regular graphs. The eigenvalues of the adjacency matrices of such graphs are well known and it is of interest to determine if any of the Tanner graphs derived from the partial geometries are good expanders for certain parameter sets, since it can be argued that codes with good geometric and expansion properties might perform well under message-passing decoding.Comment: 34 pages with single column, 6 figure

On a generalization of the pless symmetry codes

A class of matrices which are orthogonal over the reals and contain only the elements, 0, ± 1, is constructed. For certain parameters, these matrices are used to construct a class of self dual codes over GF(3). This class is shown to contain the class of symmetry codes and possesses many of their properties

Why does mutual fund performance not persist? The impact and interaction of fund flows and manager changes

This paper investigates the reasons for the lack of long-term persistence in the investment performance of actively managed equity mutual funds. We document that the responses of investors, fund managers, and investment management companies to past performance have an important impact on future performance. Conditioning on fund flows and manager changes allows us to predict future performance of both past outperforming (winner) and past underperforming (loser) funds. Recent winner funds, experiencing neither high inflows nor the departure of a skilled fund manager, outperform by 3.60 percentage points based on risk-adjusted returns in the following year, relative to winner funds suffering from both effects. We also find that the performance of the worst performing funds experiencing both the replacement of the fund manager (internal governance) and high outflows (external governance) enjoy a subsequent increase in performance of 2.40 percentage points in the following year, relative to loser funds not experiencing these effects. Among loser funds, in particular, both mechanisms appear to interact strongly.Mutual Funds; Performance Persistence; Fund Flows; Manager Turnover

Adaptive Delivery in Caching Networks

The problem of content delivery in caching networks is investigated for scenarios where multiple users request identical files. Redundant user demands are likely when the file popularity distribution is highly non-uniform or the user demands are positively correlated. An adaptive method is proposed for the delivery of redundant demands in caching networks. Based on the redundancy pattern in the current demand vector, the proposed method decides between the transmission of uncoded messages or the coded messages of [1] for delivery. Moreover, a lower bound on the delivery rate of redundant requests is derived based on a cutset bound argument. The performance of the adaptive method is investigated through numerical examples of the delivery rate of several specific demand vectors as well as the average delivery rate of a caching network with correlated requests. The adaptive method is shown to considerably reduce the gap between the non-adaptive delivery rate and the lower bound. In some specific cases, using the adaptive method, this gap shrinks by almost 50% for the average rate.Comment: 8 pages,8 figures. Submitted to IEEE transaction on Communications in 2015. A short version of this article was published as an IEEE Communications Letter with DOI: 10.1109/LCOMM.2016.255814

Two novel flight-interception trap designs for low-cost forest insect surveys

This paper introduces two passive trap designs for the survey of flying Coleoptera and other insects which can be constructed on very low budgets at < £1 per trap. A trunk window trap and an aerial flight-interception trap are presented, based on commonly used designs, but using much cheaper materials than standard. Construction diagrams are given, along with a description of trap installation, operation and beetle species found using these methods during a survey of Ayr Gorge Woodland, South-West Scotland. The traps were found to be robust and easy to operate. It is hoped that these trap designs will be of use to charitable organisations, students and amateurs who may previously have been unable to consider monitoring flying insects at large scales due to the prohibitive cost of equipment

Decentralized investment management: evidence from the pension fund industry

The past few decades have seen amajor shift from centralized to decentralized investment management by pension fund sponsors, despite the increased coordination problems that this brings. Using a unique, proprietary dataset of pension sponsors and managers, we identify two secular decentralization trends: sponsors switched (i) from generalist (balanced) to specialist managers across asset classes and (ii) from single to multiple competing managers within each asset class. We study the effect of decentralization on the risk and performance of pension funds, and find evidence supporting some predictions of recent theory on this subject. Specifically, the switch from balanced to specialist managers is motivated by the superior performance of specialists, and the switch from single to multiple managers is driven by sponsors properly anticipating diseconomies-of-scale within an asset class (as funds grow larger) and adding managers with different strategies before performance deteriorates. Indeed, we find that sponsors benefit from alpha diversification when employing multiple fund managers. Interestingly, competition between multiple specialist managers also improves performance, after controlling for size of assets and fund management company-level skill effects. We also study changes in risk-taking when moving to decentralized management. Here, we find that sponsors appear to anticipate the difficulty of coordinating multiple managers by allocating reduced risk budgets to each manager, as predicted by recent theory, which helps to compensate for the suboptimal diversification that results through an improved Sharpe ratio. Overall, our results indicate that pension fund sponsors, at least on average, rationally choose their delegation structures.Decentralized investment management; diversification loss; coordination problems; fund manager skill; pension funds

The Winnability of Klondike Solitaire and Many Other Patience Games

Our ignorance of the winnability percentage of the game in the Windows Solitaire program, more properly called 'Klondike', has been described as "one of the embarrassments of applied mathematics". Klondike is just one of many single-player card games, generically called 'patience' or 'solitaire' games, for which players have long wanted to know how likely a particular game is to be winnable. A number of different games have been studied empirically in the academic literature and by non-academic enthusiasts. Here we show that a single general purpose Artificial Intelligence program, called "Solvitaire", can be used to determine the winnability percentage of 45 different single-player card games with a 95% confidence interval of +/- 0.1% or better. For example, we report the winnability of Klondike as 81.956% +/- 0.096% (in the 'thoughtful' variant where the player knows the location of all cards), a 30-fold reduction in confidence interval over the best previous result. Almost all our results are either entirely new or represent significant improvements on previous knowledge

Ending compulsory annuitisation: what are the consequences?

The seventh in a series of reports that focus on pensions issues of direct relevance to policymakers, financial advisers, and pension scheme members.The Government intends to end the requirement for defined contribution personal pension scheme members to annuitise their pension fund by the age of 75. This report looks at the likely effects and consequences of this policy