50 research outputs found
Quantum machine learning: a classical perspective
Recently, increased computational power and data availability, as well as
algorithmic advances, have led machine learning techniques to impressive
results in regression, classification, data-generation and reinforcement
learning tasks. Despite these successes, the proximity to the physical limits
of chip fabrication alongside the increasing size of datasets are motivating a
growing number of researchers to explore the possibility of harnessing the
power of quantum computation to speed-up classical machine learning algorithms.
Here we review the literature in quantum machine learning and discuss
perspectives for a mixed readership of classical machine learning and quantum
computation experts. Particular emphasis will be placed on clarifying the
limitations of quantum algorithms, how they compare with their best classical
counterparts and why quantum resources are expected to provide advantages for
learning problems. Learning in the presence of noise and certain
computationally hard problems in machine learning are identified as promising
directions for the field. Practical questions, like how to upload classical
data into quantum form, will also be addressed.Comment: v3 33 pages; typos corrected and references adde
Compositional Performance Modelling with the TIPPtool
Stochastic process algebras have been proposed as compositional specification formalisms for performance models. In this paper, we describe a tool which aims at realising all beneficial aspects of compositional performance modelling, the TIPPtool. It incorporates methods for compositional specification as well as solution, based on state-of-the-art techniques, and wrapped in a user-friendly graphical front end. Apart from highlighting the general benefits of the tool, we also discuss some lessons learned during development and application of the TIPPtool. A non-trivial model of a real life communication system serves as a case study to illustrate benefits and limitations
Expressing mobility in process algebras: first-order and higher-order paradigms
We study mobile systems, i.e. systems with a dynamically changing communication
topology, from a process algebras point of view. Mobility can be introduced
in process algebras by allowing names or terms to be transmitted. We distinguish
these two approaches as first-order and higher-order. The major target of the
thesis is the comparison between them.
The prototypical calculus in the first-order paradigm is the Ï-calculus. By
generalising its sort discipline we derive an w-order extension called Higher-Order
Ï-calculus (HOÏ). We show that such an extension does not add expressiveness
to the Ï-calculus: Higher-order processes can be faithfully compiled down
to first-order, and respecting the behavioural equivalence we adopted in the calculi.
Such an equivalence is based on the notion of bisimulation, a fundamental
concept of process algebras. Unfortunately, the standard definition of bisimulation
is unsatisfactory in a higher-order calculus because it is over-discriminating.
To overcome the problem, we propose barbed bisimulation. Its advantage is that
it can be defined uniformly in different calculi because it only requires that the
calculus possesses an interaction or reduction relation. As a test for barbed bisimulation,
we show that in CCS and Ï-calculus, it allows us to recover the familiar
bisimulation-based equivalences. We also give simpler characterisations of the
equivalences utilised in HOÏ. For this we exploit a special kind of agents called
triggers, with which it is possible to reason fairly efficiently in a higher-order calculus
notwithstanding the complexity of its transitions.
Finally, we use the compilation from HOÏ to Ï-calculus to investigate Milner'
Hybrid programs
The MAP-i Doctoral Programme in Informatics, of the Universities of Minho, Aveiro and PortoThis thesis studies hybrid systems, an emerging family of devices that combine in their
models digital computations and physical processes. They are very quickly becoming a
main concern in software engineering, which is explained by the need to develop software
products that closely interact with physical attributes of their environment e. g. velocity,
time, energy, temperature â typical examples range from micro-sensors and pacemakers,
to autonomous vehicles, transport infrastructures and district-wide electric grids. But
even if already widespread, these systems entail different combinations of programs with
physical processes, and this renders their development a challenging task, still largely
unmet by the current programming practices.
Our goal is to address this challenge at its core; we wish to isolate the basic interactions
between discrete computations and physical processes, and bring forth the programming
paradigm that naturally underlies them. In order to do so in a precise and clean way, we
resort to monad theory, a well established categorical framework for developing program
semantics systematically. We prove the existence of a monad that naturally encodes the
aforementioned interactions, and use it to develop and examine the foundations of the
paradigm alluded above, which we call hybrid programming: we show how to build, in a
methodical way, different programming languages that accommodate amplifiers, differential
equations, and discrete assignments â the basic ingredients of hybrid systems â we list
all program operations available in the paradigm, introduce if-then-else constructs, abort
operations, and different types of feedback.
Hybrid systems bring several important aspects of control theory into computer science.
One of them is the notion of stability, which refers to a systemâs capacity of avoiding
significant changes in its output if small variations in its state or input occur. We introduce
a notion of stability to hybrid programming, explore it, and show how to analyse hybrid
programs with respect to it in a compositional manner.
We also introduce hybrid programs with internal memory and show that they form
the basis of a component-based software development discipline in hybrid programming.
We develop their coalgebraic theory, namely languages, notions of behaviour, and bisimulation.
In the process, we introduce new theoretical results on Coalgebra, including
improvements of well-known results and proofs on the existence of suitable notions of
behaviour for non-deterministic transition systems with infinite state spaces.Esta tese estuda sistemas hĂbridos, uma famĂlia emergente de dispositivos que envolvem
diferentes interaçÔes entre computaçÔes digitais e processos fĂsicos. Estes sistemas estĂŁo
rapidamente a tornar-se elementos-chave da engenharia de software, o que Ă© explicado
pela necessidade de desenvolver produtos que interagem com os atributos fĂsicos do seu
ambiente e. g. velocidade, tempo, energia, e temperatura â exemplos tĂpicos variam de
micro-sensores e pacemakers, a veĂculos autĂłnomos, infra-estruturas de transporte, e redes
eléctricas distritais. Mas ainda que amplamente usados, estes sistemas são geralmente
desenvolvidos de forma pouco sistemåtica nas pråcticas de programação atuais.
O objetivo deste trabalho é isolar as interaçÔes båsicas entre computaçÔes digitais e
processos fĂsicos, e subsequentemente desenvolver o paradigma de programação subjacente.
Para fazer isto de forma precisa, a nossa base de trabalho irĂĄ ser a teoria das
mĂłnadas, uma estrutura categĂłrica para o desenvolvimento sistemĂĄtico de semĂąnticas
na programação. A partir desta base, provamos a existĂȘncia de uma mĂłnada que capta
as interaçÔes acima mencionadas, e usamo-la para desenvolver e examinar os fundamentos
do paradigma de programação correspondente a que chamamos programação hĂbrida:
mostramos como construir, de maneira metódica, diferentes linguagens de programação
que acomodam amplificadores, equaçÔes diferenciais, e atribuiçÔes - os ingredientes båsicos
dos sistemas hĂbridos - caracterizamos todas as operaçÔes sobre programas disponĂveis,
introduzimos construçÔes if-then-else, operaçÔes para lidar com excepçÔes, e diferentes
tipos de feedback.
Os sistemas hĂbridos trazem vĂĄrios aspectos da teoria de controlo para a ciĂȘncia da
computação. Um destes é a noção de estabilidade, que se refere à capacidade de um
sistema de evitar mudanças dråsticas no seu output se pequenas variaçÔes no seu estado ou
input ocorrerem. Neste trabalho, desenvolvemos uma noção composicional de estabilidade
para a programação hĂbrida. Introduzimos tambĂ©m programas hĂbridos com memĂłria
interna, que formam a base de uma disciplina de desenvolvimento de software baseado em
componentes. Desenvolvemos a sua teoria coalgébrica, nomeadamente linguagens, noçÔes
de comportamento e bisimulação. Neste processo, introduzimos também novos resultados
teĂłricos sobre Coalgebra, incluindo melhorias a resultados conhecidos e provas acerca da
existĂȘncia de noçÔes de comportamento para sistemas de transição nĂŁo determinĂsiticos
com espaço de estados infinitos.The present work was financed by FCT â Fundação para a CiĂȘncia e a Tecnologia â
with the grant SFRH/BD/52234/2013. Additional support was provided by the PTFLAD
Chair on Smart Cities & Smart Governance and by project DalĂ (POCI-01-0145-FEDER-016692), the latter funder by ERDF â European Regional Development Fund â through COMPETE 2020 â Operational Programme for Competitiveness and Internationalisation â together with FCT
Foundations of Software Science and Computation Structures
This open access book constitutes the proceedings of the 22nd International Conference on Foundations of Software Science and Computational Structures, FOSSACS 2019, which took place in Prague, Czech Republic, in April 2019, held as part of the European Joint Conference on Theory and Practice of Software, ETAPS 2019. The 29 papers presented in this volume were carefully reviewed and selected from 85 submissions. They deal with foundational research with a clear significance for software science