2,377 research outputs found
Deep Unsupervised Similarity Learning using Partially Ordered Sets
Unsupervised learning of visual similarities is of paramount importance to
computer vision, particularly due to lacking training data for fine-grained
similarities. Deep learning of similarities is often based on relationships
between pairs or triplets of samples. Many of these relations are unreliable
and mutually contradicting, implying inconsistencies when trained without
supervision information that relates different tuples or triplets to each
other. To overcome this problem, we use local estimates of reliable
(dis-)similarities to initially group samples into compact surrogate classes
and use local partial orders of samples to classes to link classes to each
other. Similarity learning is then formulated as a partial ordering task with
soft correspondences of all samples to classes. Adopting a strategy of
self-supervision, a CNN is trained to optimally represent samples in a mutually
consistent manner while updating the classes. The similarity learning and
grouping procedure are integrated in a single model and optimized jointly. The
proposed unsupervised approach shows competitive performance on detailed pose
estimation and object classification.Comment: Accepted for publication at IEEE Computer Vision and Pattern
Recognition 201
Complexity of matrix problems
In representation theory, the problem of classifying pairs of matrices up to
simultaneous similarity is used as a measure of complexity; classification
problems containing it are called wild problems. We show in an explicit form
that this problem contains all classification matrix problems given by quivers
or posets. Then we prove that it does not contain (but is contained in) the
problem of classifying three-valent tensors. Hence, all wild classification
problems given by quivers or posets have the same complexity; moreover, a
solution of any one of these problems implies a solution of each of the others.
The problem of classifying three-valent tensors is more complicated.Comment: 24 page
Quasiplanar diagrams and slim semimodular lattices
A (Hasse) diagram of a finite partially ordered set (poset) P will be called
quasiplanar if for any two incomparable elements u and v, either v is on the
left of all maximal chains containing u, or v is on the right of all these
chains. Every planar diagram is quasiplanar, and P has a quasiplanar diagram
iff its order dimension is at most 2. A finite lattice is slim if it is
join-generated by the union of two chains. We are interested in diagrams only
up to similarity. The main result gives a bijection between the set of the
(similarity classes of) finite quasiplanar diagrams and that of the (similarity
classes of) planar diagrams of finite, slim, semimodular lattices. This
bijection allows one to describe finite posets of order dimension at most 2 by
finite, slim, semimodular lattices, and conversely. As a corollary, we obtain
that there are exactly (n-2)! quasiplanar diagrams of size n.Comment: 19 pages, 3 figure
Expressive Logics for Coinductive Predicates
The classical Hennessy-Milner theorem says that two states of an image-finite transition system are bisimilar if and only if they satisfy the same formulas in a certain modal logic. In this paper we study this type of result in a general context, moving from transition systems to coalgebras and from bisimilarity to coinductive predicates. We formulate when a logic fully characterises a coinductive predicate on coalgebras, by providing suitable notions of adequacy and expressivity, and give sufficient conditions on the semantics. The approach is illustrated with logics characterising similarity, divergence and a behavioural metric on automata
Degeneration and orbits of tuples and subgroups in an Abelian group
A tuple (or subgroup) in a group is said to degenerate to another if the
latter is an endomorphic image of the former. In a countable reduced abelian
group, it is shown that if tuples (or finite subgroups) degenerate to each
other, then they lie in the same automorphism orbit. The proof is based on
techniques that were developed by Kaplansky and Mackey in order to give an
elegant proof of Ulm's theorem. Similar results hold for reduced countably
generated torsion modules over principal ideal domains. It is shown that the
depth and the description of atoms of the resulting poset of orbits of tuples
depend only on the Ulm invariants of the module in question (and not on the
underlying ring). A complete description of the poset of orbits of elements in
terms of the Ulm invariants of the module is given. The relationship between
this description of orbits and a very different-looking one obtained by Dutta
and Prasad for torsion modules of bounded order is explained.Comment: 13 pages, 1 figur
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