658 research outputs found
A Case Study on Logical Relations using Contextual Types
Proofs by logical relations play a key role to establish rich properties such
as normalization or contextual equivalence. They are also challenging to
mechanize. In this paper, we describe the completeness proof of algorithmic
equality for simply typed lambda-terms by Crary where we reason about logically
equivalent terms in the proof environment Beluga. There are three key aspects
we rely upon: 1) we encode lambda-terms together with their operational
semantics and algorithmic equality using higher-order abstract syntax 2) we
directly encode the corresponding logical equivalence of well-typed
lambda-terms using recursive types and higher-order functions 3) we exploit
Beluga's support for contexts and the equational theory of simultaneous
substitutions. This leads to a direct and compact mechanization, demonstrating
Beluga's strength at formalizing logical relations proofs.Comment: In Proceedings LFMTP 2015, arXiv:1507.0759
Multidimensional self-affine sets: non-empty interior and the set of uniqueness
Let be a contracting matrix. In this paper we consider the
self-affine iterated function system , where is a cyclic
vector. Our main result is as follows: if , then the
attractor has non-empty interior.
We also consider the set of points in which have a
unique address. We show that unless belongs to a very special (non-generic)
class, the Hausdorff dimension of is positive. For this special
class the full description of is given as well.
This paper continues our work begun in two previous papers.Comment: 10 pages, no figure
Digit frequencies and self-affine sets with non-empty interior
In this paper we study digit frequencies in the setting of expansions in
non-integer bases, and self-affine sets with non-empty interior.
Within expansions in non-integer bases we show that if
then every has a simply
normal -expansion. We also prove that if
then every has a
-expansion for which the digit frequency does not exist, and a
-expansion with limiting frequency of zeros , where is any real
number sufficiently close to .
For a class of planar self-affine sets we show that if the horizontal
contraction lies in a certain parameter space and the vertical contractions are
sufficiently close to then every nontrivial vertical fibre contains an
interval. Our approach lends itself to explicit calculation and give rise to
new examples of self-affine sets with non-empty interior. One particular
strength of our approach is that it allows for different rates of contraction
in the vertical direction
Towards Foundational Models for Molecular Learning on Large-Scale Multi-Task Datasets
Recently, pre-trained foundation models have enabled significant advancements
in multiple fields. In molecular machine learning, however, where datasets are
often hand-curated, and hence typically small, the lack of datasets with
labeled features, and codebases to manage those datasets, has hindered the
development of foundation models. In this work, we present seven novel datasets
categorized by size into three distinct categories: ToyMix, LargeMix and
UltraLarge. These datasets push the boundaries in both the scale and the
diversity of supervised labels for molecular learning. They cover nearly 100
million molecules and over 3000 sparsely defined tasks, totaling more than 13
billion individual labels of both quantum and biological nature. In comparison,
our datasets contain 300 times more data points than the widely used OGB-LSC
PCQM4Mv2 dataset, and 13 times more than the quantum-only QM1B dataset. In
addition, to support the development of foundational models based on our
proposed datasets, we present the Graphium graph machine learning library which
simplifies the process of building and training molecular machine learning
models for multi-task and multi-level molecular datasets. Finally, we present a
range of baseline results as a starting point of multi-task and multi-level
training on these datasets. Empirically, we observe that performance on
low-resource biological datasets show improvement by also training on large
amounts of quantum data. This indicates that there may be potential in
multi-task and multi-level training of a foundation model and fine-tuning it to
resource-constrained downstream tasks
EEG To FMRI Synthesis: Is Deep Learning a Candidate?
Advances on signal, image and video generation underly major breakthroughs on generative medical imaging tasks, including Brain Image Synthesis. Still, the extent to which functional Magnetic Ressonance Imaging (fMRI) can be mapped from the brain electrophysiology remains largely unexplored. This work provides the first comprehensive view on how to use state-of-the-art principles from Neural Processing to synthesize fMRI data from electroencephalographic (EEG) data. Given the distinct spatiotemporal nature of haemodynamic and electrophysiological signals, this problem is formulated as the task of learning a mapping function between multivariate time series with highly dissimilar structures. A comparison of state-of-the-art synthesis approaches, including Autoencoders, Generative Adversarial Networks and Pairwise Learning, is undertaken. Results highlight the feasibility of EEG to fMRI brain image mappings, pinpointing the role of current advances in Machine Learning and showing the relevance of upcoming contributions to further improve performance. EEG to fMRI synthesis offers a way to enhance and augment brain image data, and guarantee access to more affordable, portable and long-lasting protocols of brain activity monitoring. The code used in this manuscript is available in Github and the datasets are open source
POPLMark reloaded: Mechanizing proofs by logical relations
We propose a new collection of benchmark problems in mechanizing the metatheory of programming languages, in order to compare and push the state of the art of proof assistants. In particular, we focus on proofs using logical relations (LRs) and propose establishing strong normalization of a simply typed calculus with a proof by Kripke-style LRs as a benchmark. We give a modern view of this well-understood problem by formulating our LR on well-typed terms. Using this case study, we share some of the lessons learned tackling this problem in different dependently typed proof environments. In particular, we consider the mechanization in Beluga, a proof environment that supports higher-order abstract syntax encodings and contrast it to the development and strategies used in general-purpose proof assistants such as Coq and Agda. The goal of this paper is to engage the community in discussions on what support in proof environments is needed to truly bring mechanized metatheory to the masses and engage said community in the crafting of future benchmarks
- …