2,016 research outputs found
Communication Cost for Updating Linear Functions when Message Updates are Sparse: Connections to Maximally Recoverable Codes
We consider a communication problem in which an update of the source message
needs to be conveyed to one or more distant receivers that are interested in
maintaining specific linear functions of the source message. The setting is one
in which the updates are sparse in nature, and where neither the source nor the
receiver(s) is aware of the exact {\em difference vector}, but only know the
amount of sparsity that is present in the difference-vector. Under this
setting, we are interested in devising linear encoding and decoding schemes
that minimize the communication cost involved. We show that the optimal
solution to this problem is closely related to the notion of maximally
recoverable codes (MRCs), which were originally introduced in the context of
coding for storage systems. In the context of storage, MRCs guarantee optimal
erasure protection when the system is partially constrained to have local
parity relations among the storage nodes. In our problem, we show that optimal
solutions exist if and only if MRCs of certain kind (identified by the desired
linear functions) exist. We consider point-to-point and broadcast versions of
the problem, and identify connections to MRCs under both these settings. For
the point-to-point setting, we show that our linear-encoder based achievable
scheme is optimal even when non-linear encoding is permitted. The theory is
illustrated in the context of updating erasure coded storage nodes. We present
examples based on modern storage codes such as the minimum bandwidth
regenerating codes.Comment: To Appear in IEEE Transactions on Information Theor
Extending the Finite Domain Solver of GNU Prolog
International audienceThis paper describes three significant extensions for the Finite Domain solver of GNU Prolog. First, the solver now supports negative integers. Second, the solver detects and prevents integer overflows from occurring. Third, the internal representation of sparse domains has been redesigned to overcome its current limitations. The preliminary performance evaluation shows a limited slowdown factor with respect to the initial solver. This factor is widely counterbalanced by the new possibilities and the robustness of the solver. Furthermore these results are preliminary and we propose some directions to limit this overhead
Executing Gödel’s programme in set theory
The study of set theory (a mathematical theory of infinite collections) has garnered
a great deal of philosophical interest since its development. There are several reasons
for this, not least because it has a deep foundational role in mathematics; any
mathematical statement (with the possible exception of a few controversial examples)
can be rendered in set-theoretic terms. However, the fruitfulness of set theory
has been tempered by two difficult yet intriguing philosophical problems: (1.) the
susceptibility of naive formulations of sets to contradiction, and (2.) the inability of
widely accepted set-theoretic axiomatisations to settle many natural questions. Both
difficulties have lead scholars to question whether there is a single, maximal Universe
of sets in which all set-theoretic statements are determinately true or false (often denoted
by ‘V ’). This thesis illuminates this discussion by showing just what is possible
on the ‘one Universe’ view. In particular, we show that there are deep relationships
between responses to (1.) and the possible tools that can be used in resolving (2.).
We argue that an interpretation of extensions of V is desirable for addressing (2.) in
a fruitful manner. We then provide critical appraisal of extant philosophical views
concerning (1.) and (2.), before motivating a strong mathematical system (known
as‘Morse-Kelley’ class theory or ‘MK’). Finally we use MK to provide a coding of
discourse involving extensions of V , and argue that it is philosophically virtuous. In
more detail, our strategy is as follows:
Chapter I (‘Introduction’) outlines some reasons to be interested in set theory
from both a philosophical and mathematical perspective. In particular, we describe
the current widely accepted conception of set (the ‘Iterative Conception’) on which
sets are formed successively in stages, and remark that set-theoretic questions can
be resolved on the basis of two dimensions: (i) how ‘high’ V is (i.e. how far we go
in forming stages), and (ii) how ‘wide’ V is (i.e. what sets are formed at successor
stages). We also provide a very coarse-grained characterisation of the set-theoretic
paradoxes and remark that extensions of universes in both height and width are relevant
for our understanding of (1.) and (2.). We then present the different motivations
for holding either a ‘one Universe’ or ‘many universes’ view of the subject matter of
set theory, and argue that there is a stalemate in the dialectic. Instead we advocate
filling out each view in its own terms, and adopt the ‘one Universe’ view for the
thesis.
Chapter II (‘G¨odel’s Programme’) then explains the Universist project for formulating
and justifying new axioms concerning V . We argue that extensions of V are
relevant to both aspects of G¨odel’s Programme for resolving independence. We also
identify a ‘Hilbertian Challenge’ to explain how we should interpret extensions of
V , given that we wish to use discourse that makes apparent reference to such nonexistent
objects.
Chapter III (‘Problematic Principles’) then lends some mathematical precision
to the coarse-grained outline of Chapter I, examining mathematical discourse that
seems to require talk of extensions of V .
Chapter IV (‘Climbing above V ?’), examines some possible interpretations of
height extensions of V . We argue that several such accounts are philosophically
problematic. However, we point out that these difficulties highlight two constraints
on resolution of the Hilbertian Challenge: (i) a Foundational Constraint that we do
not appeal to entities not representable using sets from V , and (ii) an Ontological
Constraint to interpret extensions of V in such a way that they are clearly different
from ordinary sets.
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Chapter V (‘Broadening V ’s Horizons?’), considers interpretations of width extensions.
Again, we argue that many of the extant methods for interpreting this kind
of extension face difficulties. Again, however, we point out that a constraint is highlighted;
a Methodological Constraint to interpret extensions of V in a manner that
makes sense of our naive thinking concerning extensions, and links this thought to
truth in V . We also note that there is an apparent tension between the three constraints.
Chapter VI (‘A Theory of Classes’) changes tack, and provides a positive characterisation
of apparently problematic ‘proper classes’ through the use of plural quantification.
It is argued that such a characterisation of proper class discourse performs
well with respect to the three constraints, and motivates the use of a relatively strong
class theory (namely MK).
Chapter VII (‘V -logic and Resolution’) then puts MK to work in interpreting
extensions of V . We first expand our logical resources to a system called V -logic,
and show how discourse concerning extensions can be thereby represented. We then
show how to code the required amount of V -logic usingMK. Finally, we argue that
such an interpretation performs well with respect to the three constraints.
Chapter VIII (‘Conclusions’) reviews the thesis and makes some points regarding
the exact dialectical situation. We argue that there are many different philosophical
lessons that one might take from the thesis, and are clear that we do not commit
ourselves to any one such conclusion. We finally provide some open questions and
indicate directions for future research, remarking that the thesis opens the way for
new and exciting philosophical and mathematical discussion
Hidden Markov Models
Hidden Markov Models (HMMs), although known for decades, have made a big career nowadays and are still in state of development. This book presents theoretical issues and a variety of HMMs applications in speech recognition and synthesis, medicine, neurosciences, computational biology, bioinformatics, seismology, environment protection and engineering. I hope that the reader will find this book useful and helpful for their own research
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