title: Accelerating the XGBoost algorithm using GPU computing

authors: Mitchell, Rory

subjects: computer science

abstract: We present a CUDA-based implementation of a decision tree construction algorithm within the gradient boosting library XGBoost. The tree construction algorithm is executed entirely on the graphics processing unit (GPU) and shows high performance with a variety of datasets and settings, including sparse input matrices. Individual boosting iterations are parallelised, combining two approaches. An interleaved approach is used for shallow trees, switching to a more conventional radix sort-based approach for larger depths. We show speedups of between 3x and 6x using a Titan X compared to a 4 core i7 CPU, and 1.2x using a Titan X compared to 2x Xeon CPUs (24 cores). We show that it is possible to process the Higgs dataset (10 million instances, 28 features) entirely within GPU memory. The algorithm is made available as a plug-in within the XGBoost library and fully supports all XGBoost features including classification, regression and ranking tasks.

text: Accelerating the XGBoost algorithm using GPU computing We present a CUDA-based implementation of a decision tree construction algorithm within the gradient boosting library XGBoost. The tree construction algorithm is executed entirely on the graphics processing unit (GPU) and shows high performance with a variety of datasets and settings, including sparse input matrices. Individual boosting iterations are parallelised, combining two approaches. An interleaved approach is used for shallow trees, switching to a more conventional radix sort-based approach for larger depths. We show speedups of between 3x and 6x using a Titan X compared to a 4 core i7 CPU, and 1.2x using a Titan X compared to 2x Xeon CPUs (24 cores). We show that it is possible to process the Higgs dataset (10 million instances, 28 features) entirely within GPU memory. The algorithm is made available as a plug-in within the XGBoost library and fully supports all XGBoost features including classification, regression and ranking tasks.

year: 2017

title: Civil conflict and international migration in Nepal

authors: Sharma, Hari

subjects: Civil conflict

abstract: A growing literature studies the causes and consequences of civil conflict. Several of these studies are of Nepal’s civil conflict that lasted for a decade from 1996. Coincident with this conflict was a surge in work-related emigration, affecting education and human capital investments, labour supply, and local economic activity. While a few prior studies look at the effects of Nepal’s conflict on emigration, many key features of the conflict are ignored. In particular, heterogeneity due to the highly localized nature of the conflict tends to be ignored by the type of data and research designs used in prior studies. In this thesis, I contribute to the literature on the causes and consequences of civil conflict by constructing and using very local indicators of driving forces and intensity of Nepal’s civil conflict.
Contrary to prior literature that suggests there is more conflict in poorer regions, I find poverty is associated with less conflict risk and conflict intensity, partly due to a change in strategy by the rebels in Nepal to target richer middle class and urban areas to win the war. At the same time, inequality and caste-based polarisation at local levels were major contributors that escalated the civil conflict. In order to study conflict escalation and also to study the impact of conflict intensity on migration, I construct a database of conflict deaths, and of poverty, inequality and caste polarization for almost 4000 localities. In contrast, most previous research on Nepal relies on data aggregated to the district level, suppressing detail as there are only 75 districts and there was far more variation in conflict intensity within districts than between districts. Estimated impacts of conflict on emigration are substantially distorted by using district-level conflict data.
The growth in emigration that sees over two million Nepalese working abroad has also given a great boost to remittances, which are now equivalent to about one-third of GDP. The effects of emigration and remittances on human capital investment – particularly child schooling and child labour – remain debated in the literature. I construct a two-wave panel at the locality level to study these issues, with careful attention paid to the endogeneity of emigration and to spatial spillover effects. In localities with a greater increase in emigration, the net enrolment rate in secondary education rises and child labour for older children decreases. A possible channel for this effect is that migration and remittances help credit constrained households to cover extra schooling costs and compensate for the foregone earnings from child labour. In addition to finding an overall positive effect of emigration, I find that the direct (own) effect of emigration increases labour supply of the female labour force but decreases the labour supply in the agriculture sector. There are also positive spatial spillover effects for rural localities, that likely occur through rising local wage rates.
Given these generally positive effects of emigration, the fact that local conflict intensity suppressed the growth in emigration suggests that there is a lasting negative effect of the civil conflict in particular parts of Nepal. These effects would not be apparent in the overly aggregated data on conflict that has been used to date. Thus, one contribution of this thesis is to show the benefit of a very local focus on the causes and consequences of civil conflict.

text: Civil conflict and international migration in Nepal A growing literature studies the causes and consequences of civil conflict. Several of these studies are of Nepal’s civil conflict that lasted for a decade from 1996. Coincident with this conflict was a surge in work-related emigration, affecting education and human capital investments, labour supply, and local economic activity. While a few prior studies look at the effects of Nepal’s conflict on emigration, many key features of the conflict are ignored. In particular, heterogeneity due to the highly localized nature of the conflict tends to be ignored by the type of data and research designs used in prior studies. In this thesis, I contribute to the literature on the causes and consequences of civil conflict by constructing and using very local indicators of driving forces and intensity of Nepal’s civil conflict.
Contrary to prior literature that suggests there is more conflict in poorer regions, I find poverty is associated with less conflict risk and conflict intensity, partly due to a change in strategy by the rebels in Nepal to target richer middle class and urban areas to win the war. At the same time, inequality and caste-based polarisation at local levels were major contributors that escalated the civil conflict. In order to study conflict escalation and also to study the impact of conflict intensity on migration, I construct a database of conflict deaths, and of poverty, inequality and caste polarization for almost 4000 localities. In contrast, most previous research on Nepal relies on data aggregated to the district level, suppressing detail as there are only 75 districts and there was far more variation in conflict intensity within districts than between districts. Estimated impacts of conflict on emigration are substantially distorted by using district-level conflict data.
The growth in emigration that sees over two million Nepalese working abroad has also given a great boost to remittances, which are now equivalent to about one-third of GDP. The effects of emigration and remittances on human capital investment – particularly child schooling and child labour – remain debated in the literature. I construct a two-wave panel at the locality level to study these issues, with careful attention paid to the endogeneity of emigration and to spatial spillover effects. In localities with a greater increase in emigration, the net enrolment rate in secondary education rises and child labour for older children decreases. A possible channel for this effect is that migration and remittances help credit constrained households to cover extra schooling costs and compensate for the foregone earnings from child labour. In addition to finding an overall positive effect of emigration, I find that the direct (own) effect of emigration increases labour supply of the female labour force but decreases the labour supply in the agriculture sector. There are also positive spatial spillover effects for rural localities, that likely occur through rising local wage rates.
Given these generally positive effects of emigration, the fact that local conflict intensity suppressed the growth in emigration suggests that there is a lasting negative effect of the civil conflict in particular parts of Nepal. These effects would not be apparent in the overly aggregated data on conflict that has been used to date. Thus, one contribution of this thesis is to show the benefit of a very local focus on the causes and consequences of civil conflict.

year: 2020

title: Using a digital library as a Māori language learning resource: Issues and possibilities

authors: Mato, Paora James

subjects: Digital Library

abstract: The development of electronic language learning resources, founded on digital library technology, is a capability that, to date, is largely unrealised. The Flexible Language Acquisition (FLAX) project is a digital library initiative at the University of Waikato in New Zealand. The current FLAX activities provide practice for students who are learning English as an additional language. The prospect of extending this resource to include te reo Māori is as exciting as it is groundbreaking. The outcomes of this research inform the issues and possibilities involved in creating such resources.

The World Wide Web has allowed an everyday access to the Internet, but finding and retrieving pertinent information is often a convoluted and time-consuming exercise. The normal outcome is that users are unable to take full advantage of the available resources. Digital libraries have an unprecedented power in terms of organising and storing vast amounts of information and, with built-in retrieval functionality, serve as ideal repositories. The ability to focus the information within these repositories is extremely significant because there is no longer the chaff that normally results from Internet searches. Purposeful learning activities can be presented exploiting an assortment of media and drawing on stored information that can be assembled in a range of formats. Such capacity, flexibility and diversity is normally only encountered at traditional, physical libraries.

The research includes an overview of digital libraries and some of the language learning resources that are currently available on the Internet. Since the target language is te reo Māori, a critical review on the features of kaupapa Māori theory, pedagogy and Māori pedagogy is undertaken. Using the concepts discussed in this review, the language learning activities associated with the FLAX project are analysed to determine their suitability for learning te reo Māori. Further feedback was provided by a sample group following their testing of a selection of activities that were based on text written in te reo Māori. 
 

The analysis suggests the current range of FLAX activities have more benefit to students as tools that allow practice of the learning that has been delivered in face-to-face classroom settings, rather than as a standalone language learning resource. In their present form, the main benefits of the activities predominantly rest in the way they were performed rather than in the activities themselves. Furthermore, commentary from the testing group regarded the activities as more beneficial for practicing sentence structures, grammar and punctuation, rather than actual language learning. The group generally agreed, however, that combining the activities with methods of oral and aural transmission, in te reo Māori, would certainly result in more effective language learning outcomes.

The legitimacy of digital library-based language learning activities lies in designs that promote learner-centred interaction that is consistent with best practice communicative learning theory. When the target language is te reo Māori, it is of the utmost importance that the activities are tailored to embrace a Māori world view in ways that promote the learning rather than the activity or the content.

text: Using a digital library as a Māori language learning resource: Issues and possibilities The development of electronic language learning resources, founded on digital library technology, is a capability that, to date, is largely unrealised. The Flexible Language Acquisition (FLAX) project is a digital library initiative at the University of Waikato in New Zealand. The current FLAX activities provide practice for students who are learning English as an additional language. The prospect of extending this resource to include te reo Māori is as exciting as it is groundbreaking. The outcomes of this research inform the issues and possibilities involved in creating such resources.

The World Wide Web has allowed an everyday access to the Internet, but finding and retrieving pertinent information is often a convoluted and time-consuming exercise. The normal outcome is that users are unable to take full advantage of the available resources. Digital libraries have an unprecedented power in terms of organising and storing vast amounts of information and, with built-in retrieval functionality, serve as ideal repositories. The ability to focus the information within these repositories is extremely significant because there is no longer the chaff that normally results from Internet searches. Purposeful learning activities can be presented exploiting an assortment of media and drawing on stored information that can be assembled in a range of formats. Such capacity, flexibility and diversity is normally only encountered at traditional, physical libraries.

The research includes an overview of digital libraries and some of the language learning resources that are currently available on the Internet. Since the target language is te reo Māori, a critical review on the features of kaupapa Māori theory, pedagogy and Māori pedagogy is undertaken. Using the concepts discussed in this review, the language learning activities associated with the FLAX project are analysed to determine their suitability for learning te reo Māori. Further feedback was provided by a sample group following their testing of a selection of activities that were based on text written in te reo Māori. 
 

The analysis suggests the current range of FLAX activities have more benefit to students as tools that allow practice of the learning that has been delivered in face-to-face classroom settings, rather than as a standalone language learning resource. In their present form, the main benefits of the activities predominantly rest in the way they were performed rather than in the activities themselves. Furthermore, commentary from the testing group regarded the activities as more beneficial for practicing sentence structures, grammar and punctuation, rather than actual language learning. The group generally agreed, however, that combining the activities with methods of oral and aural transmission, in te reo Māori, would certainly result in more effective language learning outcomes.

The legitimacy of digital library-based language learning activities lies in designs that promote learner-centred interaction that is consistent with best practice communicative learning theory. When the target language is te reo Māori, it is of the utmost importance that the activities are tailored to embrace a Māori world view in ways that promote the learning rather than the activity or the content.

year: 2009