Near Optimal Parallel Algorithms for Dynamic DFS in Undirected Graphs

Depth first search (DFS) tree is a fundamental data structure for solving graph problems. The classical algorithm [SiComp74] for building a DFS tree requires $O(m+n)$ time for a given graph $G$ having $n$ vertices and $m$ edges. Recently, Baswana et al. [SODA16] presented a simple algorithm for updating DFS tree of an undirected graph after an edge/vertex update in $\tilde{O}(n)$ time. However, their algorithm is strictly sequential. We present an algorithm achieving similar bounds, that can be adopted easily to the parallel environment. In the parallel model, a DFS tree can be computed from scratch using $m$ processors in expected $\tilde{O}(1)$ time [SiComp90] on an EREW PRAM, whereas the best deterministic algorithm takes $\tilde{O}(\sqrt{n})$ time [SiComp90,JAlg93] on a CRCW PRAM. Our algorithm can be used to develop optimal (upto polylog n factors deterministic algorithms for maintaining fully dynamic DFS and fault tolerant DFS, of an undirected graph. 1- Parallel Fully Dynamic DFS: Given an arbitrary online sequence of vertex/edge updates, we can maintain a DFS tree of an undirected graph in $\tilde{O}(1)$ time per update using $m$ processors on an EREW PRAM. 2- Parallel Fault tolerant DFS: An undirected graph can be preprocessed to build a data structure of size O(m) such that for a set of $k$ updates (where $k$ is constant) in the graph, the updated DFS tree can be computed in $\tilde{O}(1)$ time using $n$ processors on an EREW PRAM. Moreover, our fully dynamic DFS algorithm provides, in a seamless manner, nearly optimal (upto polylog n factors) algorithms for maintaining a DFS tree in semi-streaming model and a restricted distributed model. These are the first parallel, semi-streaming and distributed algorithms for maintaining a DFS tree in the dynamic setting.Comment: Accepted to appear in SPAA'17, 32 Pages, 5 Figure

WaterWorks: a decision support tool for irrigation infrastructure decisions at farm level

Increasing water scarcity, climate change and pressure to provide water for environmental flows urge irrigators to be more efficient. In Australia, ongoing water reforms and most recent National Water Security Plan offer incentives to irrigators to adjust their farming practices by adopting water saving irrigation infrastructures to match with soils, crop and climatic conditions. WaterWorks is a decision support tool to facilitate irrigators to make long and short term irrigation infrastructure investment decision at the farm level. It assists irrigators to improve the economic efficiency, water use efficiency and environmental performance of their farm businesses. The WaterWorks has been tested, validated and accepted by the irrigation community and reachers in NSW. The interface of WaterWorks is user-friendly and flexible. The simulation and optimisation module in WaterWorks provides an opportunity to evaluate infrastructure investment decisions to suit their seasonal or long-term water availability. The sensitivity analysis allows substantiating the impact of major variables. Net present value, internal rate of return, benefit cost ratio and payback period are used to analyse the costs and benefits of modern irrigation technology. Application of WaterWorks using a whole farm-level case study indicates its effectiveness in making long term and short term investment decisions. The WaterWorks can be easily integrated into commercial software such as spreadsheets, GIS, real time data acquisition and control systems to further enhance its usability. The WaterWorks can also be used in regional development plannin

Role of aquifer storage and recovery for harmonising irrigation with environment in connected systems

The flows in regulated rivers are strongly dependent on water demand by downstream water users. In irrigated catchments the river flow regimes are alerted to cater for crop demand. The impacts of these altered flows can have significant deleterious ecological impacts. There can be a number of opportunities to manipulate irrigation demand and supply in a way which provide better seasonality of flows and optimise the social, environmental and economic outcomes from water use in a catchment. This paper explores groundwater – surface water substitution as possible way to change water demand patterns. Results of a modelling study show that conjunctive water use through more groundwater extraction or infiltration and extraction is also realistic option capable of replacing over 215GL of peak period surface water use with minimum cost to overall agriculture return. To secure 215GL of water through an aquifer storage and recovery program would cost around $8.96 million

Relative price changes and the growth of the public sector

Policy recommendations to reduce the growth of public spending are haunted by the inevitability of two factors. First Wagner's law, the hypothesis that with economic development an increasing share of GDP is devoted to public spending, and secondly, Baumol's effect, that as economies develop, public sector prices rise faster than prices in the general economy. Neither of these hypotheses has adequately been tested, largely because consistent public sector prices are unavailable for most developing countries. This paper proposes that the unavailability of consistent public sector price deflators can be overcome by econometrically estimating these series with the help of data on public spending and the widely available GDP deflator. This paper presents an anaylsis of time series data from 71 countries. The paper finds that although data support Wagner's law in the majority of developing countries, the degree of support varies with the level of development. Similarly, the average income elasticity of public spending drops from the low income economies through to the industrial economies. In the long run, the size of the public sector tapers off as the economies develop.Inequality,Environmental Economics&Policies,Economic Theory&Research,Achieving Shared Growth,National Governance

Design of rate-adaptive MAC and medium aware routing protocols for multi-rate, multi-hop wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result these factors are not considered which result in severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput

Quantifying Climate and Management Impacts on Watertables and Soil Salinity (Summary)

This report describes the development of a surface-groundwater interaction model for the Murrumbidgee Irrigation Area (MIA), situated in New South Wales, about 600 km west of Sydney and 900 km east of Adelaide. The MIA includes the town of Griffith and Leeton, and the study area covers the boundaries of 375250, 6150500 and 460000, 6230000 in UTM coordinate system shown in Figure E-1. On July 13, 1912 the irrigation scheme was opened bringing water to the area from storages (Burrinjuck dam – 1026 GL and Blowering dam – 1628 GL) through rivers and supply channels, using gravity as the means to manage water flow. Rice growing started in 1924 with its rapid development during 1970-80s. The total area for the MIA is 230,222 ha having dominant land use of rice with more than 32,000 ha in year 2000. Water use by crops is presented in Table E-1. The rising watertable and salinisation have threatened the viability of the MIA and this work is part of management strategies to ensure the sustainability of the area

Extending the HELP approach through the system harmonisation philosophy

The sustainable management of the water resource will become more and more important as population demands and environmental custodianship awareness grows. The Hydrology for the Environment, Life and Policy (HELP) program aims to bring together scientific research in catchment management with practical application of policy and on-ground management practices. This paper builds on an existing foundation of knowledge and exposure, within the Murrumbidgee HELP catchment already recognised as a leader finding real solutions while working with multiple stakeholders. The HELP program has now moved into the implementation stage and includes 67 catchments from around the world that are looking to better utilise their water resources for sustainable communities. Of those 67 basins there are 7 demonstration basins, one of which is the Murrumbidgee. There is a need for extending HELP to non-HELP basins through lessons learnt from existing efforts. In this context System Harmonisation Framework is introduced as an integrative framework for extending HELP in irrigated catchments across the globe.The ‘System Harmonisation’ philosophy seeks to identify business opportunities for irrigators to become an integral part of an expanding environmental services industry and in so doing support a truly sustainable and diversified irrigation business environment. A good understanding of system wide harmonisation can be gained from how irrigation systems are linked with the catchment water cycle and how life support systems and regional economies depend on them. The system harmonisation framework involves an all encompassing approach that combines research and business principles to achieve productive and environmental improvements at the catchment level. The framework involves five feasibility steps including three research components and a business analysis component: The research components comprise analysis and characterisation of hydrologic systems, water productivity, markets and ecosystem services, and mechanisms and processes for change. The business component is based on the formation of Regional Irrigation Business Partnerships (RIBP) to explore and implement opportunities for improved productive and/or environmental outcomes through changes in water management. The system harmonisation process establishes the base physical, economic and social position of the region, identifies the key pressure points in the system and the system constraint. System harmonisation thus offers great opportunity for extending HELP to other catchments around the globe to enhance the multifunctional productivity of water resources.Keywords: environmental services, multifunctional water productivity, sustainability, system harmonisatio

Optimal Construction of Hierarchical Overlap Graphs

Genome assembly is a fundamental problem in Bioinformatics, where for a given set of overlapping substrings of a genome, the aim is to reconstruct the source genome. The classical approaches to solving this problem use assembly graphs, such as de Bruijn graphs or overlap graphs, which maintain partial information about such overlaps. For genome assembly algorithms, these graphs present a trade-off between overlap information stored and scalability. Thus, Hierarchical Overlap Graph (HOG) was proposed to overcome the limitations of both these approaches. For a given set P of n strings, the first algorithm to compute HOG was given by Cazaux and Rivals [IPL20] requiring O(||P||+n²) time using superlinear space, where ||P|| is the cumulative sum of the lengths of strings in P. This was improved by Park et al. [SPIRE20] to O(||P||log n) time and O(||P||) space using segment trees, and further to O(||P||(log n)/(log log n)) for the word RAM model. Both these results described an open problem to compute HOG in optimal O(||P||) time and space. In this paper, we achieve the desired optimal bounds by presenting a simple algorithm that does not use any complex data structures. At its core, our solution improves the classical result [IPL92] for a special case of the All Pairs Suffix Prefix (APSP) problem from O(||P||+n²) time to optimal O(||P||) time, which may be of independent interest.Peer reviewe

Confidence Propagation through CNNs for Guided Sparse Depth Regression

Generally, convolutional neural networks (CNNs) process data on a regular grid, e.g. data generated by ordinary cameras. Designing CNNs for sparse and irregularly spaced input data is still an open research problem with numerous applications in autonomous driving, robotics, and surveillance. In this paper, we propose an algebraically-constrained normalized convolution layer for CNNs with highly sparse input that has a smaller number of network parameters compared to related work. We propose novel strategies for determining the confidence from the convolution operation and propagating it to consecutive layers. We also propose an objective function that simultaneously minimizes the data error while maximizing the output confidence. To integrate structural information, we also investigate fusion strategies to combine depth and RGB information in our normalized convolution network framework. In addition, we introduce the use of output confidence as an auxiliary information to improve the results. The capabilities of our normalized convolution network framework are demonstrated for the problem of scene depth completion. Comprehensive experiments are performed on the KITTI-Depth and the NYU-Depth-v2 datasets. The results clearly demonstrate that the proposed approach achieves superior performance while requiring only about 1-5% of the number of parameters compared to the state-of-the-art methods.Comment: 14 pages, 14 Figure