76,746 research outputs found
Inspecting class hierarchies in classification-based metric learning models
Most classification models treat all misclassifications equally. However,
different classes may be related, and these hierarchical relationships must be
considered in some classification problems. These problems can be addressed by
using hierarchical information during training. Unfortunately, this information
is not available for all datasets. Many classification-based metric learning
methods use class representatives in embedding space to represent different
classes. The relationships among the learned class representatives can then be
used to estimate class hierarchical structures. If we have a predefined class
hierarchy, the learned class representatives can be assessed to determine
whether the metric learning model learned semantic distances that match our
prior knowledge. In this work, we train a softmax classifier and three metric
learning models with several training options on benchmark and real-world
datasets. In addition to the standard classification accuracy, we evaluate the
hierarchical inference performance by inspecting learned class representatives
and the hierarchy-informed performance, i.e., the classification performance,
and the metric learning performance by considering predefined hierarchical
structures. Furthermore, we investigate how the considered measures are
affected by various models and training options. When our proposed ProxyDR
model is trained without using predefined hierarchical structures, the
hierarchical inference performance is significantly better than that of the
popular NormFace model. Additionally, our model enhances some
hierarchy-informed performance measures under the same training options. We
also found that convolutional neural networks (CNNs) with random weights
correspond to the predefined hierarchies better than random chance.Comment: The main manuscript is 22 pages. The whole paper is 49 pages. The
codes for our experiments will be available in
https://github.com/hjk92g/Inspecting_Hierarchies_ML . The plankton datasets
are available from the Norwegian Marine Data Center (MicroS:
https://doi.org/10.21335/NMDC-2102309336 , MicroL:
https://doi.org/10.21335/NMDC-573815973 , MesoZ:
https://doi.org/10.21335/NMDC-1805578916
Zipf's law, Hierarchical Structure, and Shuffling-Cards Model for Urban Development
A new angle of view is proposed to find the simple rules dominating complex
systems and regular patterns behind random phenomena such as cities. Hierarchy
of cities reflects the ubiquitous structure frequently observed in the natural
world and social institutions. Where there is a hierarchy with cascade
structure, there is a rank-size distribution following Zipf's law, and vice
versa. The hierarchical structure can be described with a set of exponential
functions that are identical in form to Horton-Strahler's laws on rivers and
Gutenberg-Richter's laws on earthquake energy. From the exponential models, we
can derive four power laws such as Zipf's law indicative of fractals and
scaling symmetry. Research on the hierarchy is revealing for us to understand
how complex systems are self-organized. A card-shuffling model is built to
interpret the relation between Zipf's law and hierarchy of cities. This model
can be expanded to explain the general empirical power-law distributions across
the individual physical and social sciences, which are hard to be comprehended
within the specific scientific domains.Comment: 28 pages, 8 figure
A study of hierarchical and flat classification of proteins
Automatic classification of proteins using machine learning is an important problem that has received significant attention in the literature. One feature of this problem is that expert-defined hierarchies of protein classes exist and can potentially be exploited to improve classification performance. In this article we investigate empirically whether this is the case for two such hierarchies. We compare multi-class classification techniques that exploit the information in those class hierarchies and those that do not, using logistic regression, decision trees, bagged decision trees, and support vector machines as the underlying base learners. In particular, we compare hierarchical and flat variants of ensembles of nested dichotomies. The latter have been shown to deliver strong classification performance in multi-class settings. We present experimental results for synthetic, fold recognition, enzyme classification, and remote homology detection data. Our results show that exploiting the class hierarchy improves performance on the synthetic data, but not in the case of the protein classification problems. Based on this we recommend that strong flat multi-class methods be used as a baseline to establish the benefit of exploiting class hierarchies in this area
GRASS: Generative Recursive Autoencoders for Shape Structures
We introduce a novel neural network architecture for encoding and synthesis
of 3D shapes, particularly their structures. Our key insight is that 3D shapes
are effectively characterized by their hierarchical organization of parts,
which reflects fundamental intra-shape relationships such as adjacency and
symmetry. We develop a recursive neural net (RvNN) based autoencoder to map a
flat, unlabeled, arbitrary part layout to a compact code. The code effectively
captures hierarchical structures of man-made 3D objects of varying structural
complexities despite being fixed-dimensional: an associated decoder maps a code
back to a full hierarchy. The learned bidirectional mapping is further tuned
using an adversarial setup to yield a generative model of plausible structures,
from which novel structures can be sampled. Finally, our structure synthesis
framework is augmented by a second trained module that produces fine-grained
part geometry, conditioned on global and local structural context, leading to a
full generative pipeline for 3D shapes. We demonstrate that without
supervision, our network learns meaningful structural hierarchies adhering to
perceptual grouping principles, produces compact codes which enable
applications such as shape classification and partial matching, and supports
shape synthesis and interpolation with significant variations in topology and
geometry.Comment: Corresponding author: Kai Xu ([email protected]
A Hierarchical Allometric Scaling Analysis of Chinese Cities: 1991-2014
The law of allometric scaling based on Zipf distributions can be employed to
research hierarchies of cities in a geographical region. However, the
allometric patterns are easily influenced by random disturbance from the noises
in observational data. In theory, both the allometric growth law and Zipf's law
are related to the hierarchical scaling laws associated with fractal structure.
In this paper, the scaling laws of hierarchies with cascade structure are used
to study Chinese cities, and the method of R/S analysis is applied to analyzing
the change trend of the allometric scaling exponents. The results show that the
hierarchical scaling relations of Chinese cities became clearer and clearer
from 1991 to 2014 year; the global allometric scaling exponent values
fluctuated around 0.85, and the local scaling exponent approached to 0.85. The
Hurst exponent of the allometric parameter change is greater than 0.5,
indicating persistence and a long-term memory of urban evolution. The main
conclusions can be reached as follows: the allometric scaling law of cities
represents an evolutionary order rather than an invariable rule, which emerges
from self-organized process of urbanization, and the ideas from allometry and
fractals can be combined to optimize spatial and hierarchical structure of
urban systems in future city planning.Comment: 28 pages, 10 figures, 5 table
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