Binding and Normalization of Binary Sparse Distributed Representations by Context-Dependent Thinning

Distributed representations were often criticized as inappropriate for encoding of data with a complex structure. However Plate's Holographic Reduced Representations and Kanerva's Binary Spatter Codes are recent schemes that allow on-the-fly encoding of nested compositional structures by real-valued or dense binary vectors of fixed dimensionality. In this paper we consider procedures of the Context-Dependent Thinning which were developed for representation of complex hierarchical items in the architecture of Associative-Projective Neural Networks. These procedures provide binding of items represented by sparse binary codevectors (with low probability of 1s). Such an encoding is biologically plausible and allows a high storage capacity of distributed associative memory where the codevectors may be stored. In contrast to known binding procedures, Context-Dependent Thinning preserves the same low density (or sparseness) of the bound codevector for varied number of component codevectors. Besides, a bound codevector is not only similar to another one with similar component codevectors (as in other schemes), but it is also similar to the component codevectors themselves. This allows the similarity of structures to be estimated just by the overlap of their codevectors, without retrieval of the component codevectors. This also allows an easy retrieval of the component codevectors. Examples of algorithmic and neural-network implementations of the thinning procedures are considered. We also present representation examples for various types of nested structured data (propositions using role-filler and predicate-arguments representation schemes, trees, directed acyclic graphs) using sparse codevectors of fixed dimension. Such representations may provide a fruitful alternative to the symbolic representations of traditional AI, as well as to the localist and microfeature-based connectionist representations

Representation and processing of structures with binary sparse distributed codes

The schemes for compositional distributed representations include those allowing on-the-fly construction of fixed dimensionality codevectors to encode structures of various complexity. Similarity of such codevectors takes into account both structural and semantic similarity of represented structures. In this paper we provide a comparative description of sparse binary distributed representation developed in the frames of the Associative-Projective Neural Network architecture and more well-known Holographic Reduced Representations of Plate and Binary Spatter Codes of Kanerva. The key procedure in Associative-Projective Neural Networks is Context-Dependent Thinning which binds codevectors and maintains their sparseness. The codevectors are stored in structured memory array which can be realized as distributed auto-associative memory. Examples of distributed representation of structured data are given. Fast estimation of similarity of analogical episodes by the overlap of their codevectors is used in modeling of analogical reasoning for retrieval of analogs from memory and for analogical mapping

Shift-Equivariant Similarity-Preserving Hypervector Representations of Sequences

Hyperdimensional Computing (HDC), also known as Vector-Symbolic Architectures (VSA), is a promising framework for the development of cognitive architectures and artificial intelligence systems, as well as for technical applications and emerging neuromorphic and nanoscale hardware. HDC/VSA operate with hypervectors, i.e., neural-like distributed vector representations of large fixed dimension (usually &gt; 1000). One of the key ingredients of HDC/VSA are the methods for encoding various data types (from numeric scalars and vectors to graphs) by hypervectors. In this paper, we propose an approach for the formation of hypervectors of sequences that provides both an equivariance with respect to the shift of sequences and preserves the similarity of sequences with identical elements at nearby positions. Our methods represent the sequence elements by compositional hypervectors and exploit permutations of hypervectors for representing the order of sequence elements. We experimentally explored the proposed representations using a diverse set of tasks with data in the form of symbolic strings. Although we did not use any features here (hypervector of a sequence was formed just from the hypervectors of its symbols at their positions), the proposed approach demonstrated the performance on a par with the methods that exploit various features, such as subsequences. The proposed techniques were designed for the HDC/VSA model known as Sparse Binary Distributed Representations. However, they can be adapted to hypervectors in formats of other HDC/VSA models, as well as for representing sequences of types other than symbolic strings. Directions for further research are discussed.Validerad;2024;Nivå 2;2024-06-07 (joosat);Funder: Swedish Foundation for Strategic Research (UKR22-0024, GU 2022/1963);Full text license: CC BY</p

Binding and Normalization of Binary Sparse Distributed Representations by Context-Dependent Thinning

Distributed representations were often criticized as inappropriate for encoding of data with a complex structure. However Plate's Holographic Reduced Representations and Kanerva's Binary Spatter Codes are recent schemes that allow on-the-fly encoding of nested compositional structures by real-valued or dense binary vectors of fixed dimensionality. In this paper we consider procedures of the Context-Dependent Thinning which were developed for representation of complex hierarchical items in the architecture of Associative-Projective Neural Networks. These procedures provide binding of items represented by sparse binary codevectors (with low probability of 1s). Such an encoding is biologically plausible and allows to reach high information capacity of distributed associative memory where the codevectors may be stored. In distinction to known binding procedures, Context-Dependent Thinning allows to support the same low density (or sparseness) of the bound codevector for varied number of constituent codevectors. Besides, a bound codevector is not only similar to another one with similar constituent codevectors (as in other schemes), but it is also similar to the constituent codevectors themselves. This allows to estimate a structure similarity just by the overlap of codevectors, without the retrieval of the constituent codevectors. This also allows an easy retrieval of the constituent codevectors. Examples of algorithmic and neural network implementations of the thinning procedures are considered. We also present representation examples of various types of nested structured data (propositions using role-filler and predicate-arguments representation, trees, directed acyclic graphs) using sparse codevectors of fixed dimension. Such representations may provide a fruitful alternative to the symbolic representations of traditional AI, as well as to the localist and microfeature-based connectionist representations

Application of Random Threshold Neural Networks for Diagnostics of Micro Machine Tool Condition

Micro equipment based manufacturing requires a higher automation level than traditional manufacturing, because a human operator should be able to supervise the parallel operation of many micro equipment units. We briefly describe the prototypes of micro machine tools and the random threshold neural network classifiers created by us for the experimental investigation of problems on the way to fully automated micro manufacturing. The problems of diagnostics of micro machine tools and machining modes are discussed as well as the results of experiments with the acoustic diagnostics of cutting modes using the random threshold classifier

On Possible ACD Application for Optimization of Cutting and Assembly in Mechanical Engineering

Application of adaptive critic designs for optimization of real-world processes require a model of the process under optimization or feedback from the real process. For optimization of mechanical manufacturing it is often too expensive and time consuming to use real equipment for the model. However, mathematical models adequately describing real manufacturing processes with realistic noise and interference assumptions may be too difficult to create. We propose to use micro machine tools and micro manipulators as the physical models of real mechanical engineering equipment. They allow us to reduce the cost of experiments and accelerate their speed. We have created prototypes of micro machine tools and work on their use for adaptive critic based optimal control. We describe possible use of adaptive critic designs for optimization of two typical problems of mechanical engineering: shaft cutting and gear fitting on an axle

USING RANDOMIZED ALGORITHMS FOR SOLVING DISCRETE ILL-POSED PROBLEMS

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