56 research outputs found
Return of the features. Efficient feature selection and interpretation for photometric redshifts
The explosion of data in recent years has generated an increasing need for
new analysis techniques in order to extract knowledge from massive datasets.
Machine learning has proved particularly useful to perform this task. Fully
automatized methods have recently gathered great popularity, even though those
methods often lack physical interpretability. In contrast, feature based
approaches can provide both well-performing models and understandable
causalities with respect to the correlations found between features and
physical processes. Efficient feature selection is an essential tool to boost
the performance of machine learning models. In this work, we propose a forward
selection method in order to compute, evaluate, and characterize better
performing features for regression and classification problems. Given the
importance of photometric redshift estimation, we adopt it as our case study.
We synthetically created 4,520 features by combining magnitudes, errors, radii,
and ellipticities of quasars, taken from the SDSS. We apply a forward selection
process, a recursive method in which a huge number of feature sets is tested
through a kNN algorithm, leading to a tree of feature sets. The branches of the
tree are then used to perform experiments with the random forest, in order to
validate the best set with an alternative model. We demonstrate that the sets
of features determined with our approach improve the performances of the
regression models significantly when compared to the performance of the classic
features from the literature. The found features are unexpected and surprising,
being very different from the classic features. Therefore, a method to
interpret some of the found features in a physical context is presented. The
methodology described here is very general and can be used to improve the
performance of machine learning models for any regression or classification
task.Comment: 21 pages, 11 figures, accepted for publication on A&A, final version
after language revisio
Big Universe, Big Data: Machine Learning and Image Analysis for Astronomy
Astrophysics and cosmology are rich with data. The advent of wide-area
digital cameras on large aperture telescopes has led to ever more ambitious
surveys of the sky. Data volumes of entire surveys a decade ago can now be
acquired in a single night and real-time analysis is often desired. Thus,
modern astronomy requires big data know-how, in particular it demands highly
efficient machine learning and image analysis algorithms. But scalability is
not the only challenge: Astronomy applications touch several current machine
learning research questions, such as learning from biased data and dealing with
label and measurement noise. We argue that this makes astronomy a great domain
for computer science research, as it pushes the boundaries of data analysis. In
the following, we will present this exciting application area for data
scientists. We will focus on exemplary results, discuss main challenges, and
highlight some recent methodological advancements in machine learning and image
analysis triggered by astronomical applications
Massively-Parallel Break Detection for Satellite Data
The field of remote sensing is nowadays faced with huge amounts of data.
While this offers a variety of exciting research opportunities, it also yields
significant challenges regarding both computation time and space requirements.
In practice, the sheer data volumes render existing approaches too slow for
processing and analyzing all the available data. This work aims at accelerating
BFAST, one of the state-of-the-art methods for break detection given satellite
image time series. In particular, we propose a massively-parallel
implementation for BFAST that can effectively make use of modern parallel
compute devices such as GPUs. Our experimental evaluation shows that the
proposed GPU implementation is up to four orders of magnitude faster than the
existing publicly available implementation and up to ten times faster than a
corresponding multi-threaded CPU execution. The dramatic decrease in running
time renders the analysis of significantly larger datasets possible in seconds
or minutes instead of hours or days. We demonstrate the practical benefits of
our implementations given both artificial and real datasets.Comment: 10 page
Short-term wind energy forecasting using support vector regression
Abstract Wind energy prediction has an important part to play in a smart energy grid for load balancing and capacity planning. In this paper we explore, if wind measurements based on the existing infrastructure of windmills in neighbored wind parks can be learned with a soft computing approach for wind energy prediction in the ten-minute to six-hour range. For this sake we employ Support Vector Regression (SVR) for time series forecasting, and run experimental analyses on real-world wind data from the NREL western wind resource dataset. In the experimental part of the paper we concentrate on loss function parameterization of SVR. We try to answer how far ahead a reliable wind forecast is possible, and how much information from the past is necessary. We demonstrate the capabilities of SVR-based wind energy forecast on the micro-scale level of one wind grid point, and on the larger scale of a whole wind park
Attention as Activation
Activation functions and attention mechanisms are typically treated as having
different purposes and have evolved differently. However, both concepts can be
formulated as a non-linear gating function. Inspired by their similarity, we
propose a novel type of activation units called attentional activation (ATAC)
units as a unification of activation functions and attention mechanisms. In
particular, we propose a local channel attention module for the simultaneous
non-linear activation and element-wise feature refinement, which locally
aggregates point-wise cross-channel feature contexts. By replacing the
well-known rectified linear units by such ATAC units in convolutional networks,
we can construct fully attentional networks that perform significantly better
with a modest number of additional parameters. We conducted detailed ablation
studies on the ATAC units using several host networks with varying network
depths to empirically verify the effectiveness and efficiency of the units.
Furthermore, we compared the performance of the ATAC units against existing
activation functions as well as other attention mechanisms on the CIFAR-10,
CIFAR-100, and ImageNet datasets. Our experimental results show that networks
constructed with the proposed ATAC units generally yield performance gains over
their competitors given a comparable number of parameters
Attentional Feature Fusion
Feature fusion, the combination of features from different layers or
branches, is an omnipresent part of modern network architectures. It is often
implemented via simple operations, such as summation or concatenation, but this
might not be the best choice. In this work, we propose a uniform and general
scheme, namely attentional feature fusion, which is applicable for most common
scenarios, including feature fusion induced by short and long skip connections
as well as within Inception layers. To better fuse features of inconsistent
semantics and scales, we propose a multi-scale channel attention module, which
addresses issues that arise when fusing features given at different scales. We
also demonstrate that the initial integration of feature maps can become a
bottleneck and that this issue can be alleviated by adding another level of
attention, which we refer to as iterative attentional feature fusion. With
fewer layers or parameters, our models outperform state-of-the-art networks on
both CIFAR-100 and ImageNet datasets, which suggests that more sophisticated
attention mechanisms for feature fusion hold great potential to consistently
yield better results compared to their direct counterparts. Our codes and
trained models are available online.Comment: Accepted by WACV 202
Detecting Quasars in Large-Scale Astronomical Surveys
We present a classification-based approach to identify quasi-stellar radio
sources (quasars) in the Sloan Digital Sky Survey and evaluate its performance
on a manually labeled training set. While reasonable results can already be
obtained via approaches working only on photometric data, our experiments
indicate that simple but problem-specific features extracted from spectroscopic
data can significantly improve the classification performance. Since our
approach works orthogonal to existing classification schemes used for building
the spectroscopic catalogs, our classification results are well suited for a
mutual assessment of the approaches' accuracies.Comment: 6 pages, 8 figures, published in proceedings of 2010 Ninth
International Conference on Machine Learning and Applications (ICMLA) of the
IEE
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