Gloria Galán-Marín

An Efficient Multivalued Hopfield Network for the Traveling Salesman Problem

In this Letter we show that discrete multivalued Hopfield-type neural networks enable a relatively easy formulation of the Traveling Salesman Problem compared to the traditional Hopfield model. Thus, with the multivalued representation the network can be easily confined to feasible solutions, avoiding the need to tune any parameter. An investigation into the performance of the network has led us to define updating rules based on simple effective heuristic algorithms, a technique that can not be usually incorporated into standard Hopfield models. Simulation results for Euclidean Traveling Salesman Problems taken from the data library TSPLIB [11] indicate that this multivalued neural approach is superior to the best neural network currently reported for this problem.

Modelling competitive Hopfield networks for the maximum clique problem

The maximum clique problem (MCP) is a classic graph optimization problem with many real-world applications. This problem is NP-complete and computationally intractable even to approximate with certain absolute performance bounds. In this paper, we present the design of a new discrete competitive Hopfield neural network for finding near-optimum solutions for the MCP. Other competitive Hopfield-style networks have been proposed to solve the MCP. However, recent results have shown that these models can sometimes lead to inaccurate results and oscillatory behaviors in the convergence process. Thus, the network sometimes does not converge to cliques of the considered graph, where this error usually increases with the size and the density of the graph. In contrast, we propose in this paper appropriate dynamics for a binary competitive Hop-field network in order to always generate local/global minimum points corresponding to maximal/maximun cliques of the considered graph. Moreover, an optimal modelling of the network is developed, resulting in a fast two-level winner-take-all scheme. Extensive simulation runs show that our network performs better than the other competitive neural approaches in terms of the solution quality and the computation time.

Improving Neural Networks for Mechanism Kinematic Chain Isomorphism Identification

Detection of isomorphism among kinematic chains is essential in mechanical design, but difficult and computationally expensive. It has been shown that both traditional methods and previously presented neural networks still have a lot to be desired in aspects such as simplifying procedure of identification and adapting automatic computation. Therefore, a new algorithm based on a competitive Hopfield network is developed for automatic computation in the kinematic chain isomorphism problem. The neural approach provides directly interpretable solutions and does not demand tuning of parameters. We have tested the algorithm by solving problems reported in the recent mechanical literature. Simulation results show the effectiveness of the network that rapidly identifies isomorphic kinematic chains.

A New Multivalued Neural Network for Isomorphism Identification of Kinematic Chains

A lot of methods have been proposed for the kinematic chain isomorphism problem. However, the tool is still needed in building intelligent systems for product design and manufacturing. In this paper, we design a novel multivalued neural network that enables a simplified formulation of the graph isomorphism problem. In order to improve the performance of the model, an additional constraint on the degree of paired vertices is imposed. The resulting discrete neural algorithm converges rapidly under any set of initial conditions and does not need parameter tuning. Simulation results show that the proposed multivalued neural network performs better than other recently presented approaches.

K-pages graph drawing with multivalued neural networks

In this paper, the K-pages graph layout problem is solved by a new neural model. This model consists of two neural networks performing jointly in order to minimize the same energy function. The neural technique applied to this problem allows to reduce the energy function by changing outputs from both networks -outputs of first network representing location of nodes in the nodes line, while the outputs of the second one meaning the page where the edges are drawn. A detailed description of the model is presented, and the technique to minimize an energy function is fully described. It has proved to be a very competitive and efficient algorithm, in terms of quality of solutions and computational time, when compared to the state-of-the-art heuristic methods specifically designed for this problem. Some simulation results are presented in this paper, to show the comparative efficiency of the methods.

A Study into the Improvement of Binary Hopfield Networks for Map Coloring

The map-coloring problem is a well known combinatorial optimization problem which frequently appears in mathematics, graph theory and artificial intelligence. This paper presents a study into the performance of some binary Hopfield networks with discrete dynamics for this classic problem. A number of instances have been simulated to demonstrate that only the proposed binary model provides optimal solutions. In addition, for large-scale maps an algorithm is presented to improve the local minima of the network by solving gradually growing submaps of the considered map. Simulation results for several n-region 4-color maps showed that the proposed neural algorithm converged to a correct colouring from at least 90% of initial states without the fine-tuning of parameters required in another Hopfield models.

Improved Production of Competitive Learning Rules with an Additional Term for Vector Quantization

In this work, a general framework for developing learning rules with an added term (perturbation term) is presented. Many learning rules commonly cited in the specialized literature can be derived from this general framework. This framework allows us to introduce some knowledge about vector quantization (as an optimization problem) in the distortion function in order to derive a new learning rule that uses that information to avoid certain local minima of the distortion function, leading to better performance than classical models. Computational experiments in image compression show that our proposed rule, derived from this general framework, can achieve better results than simple competitive learning and other models, with codebooks of less distortion.

A methodology to learn designing optimal mechanisms for path generation

The study of four‐bar linkages to trace a desired path is an important part of teaching in mechanical design. When the number of precision points exceeds a certain number, most recent approaches utilize intelligent optimization methods based on too complex computer science theories to be implemented by an engineering student. In this article we develop and implement new mechanism design results, reducing simultaneously the design space to facilitate finding the optimal mechanism. Finally, we apply global optimization methods that do not require analytical expression of the objective function and are freely available for educational use with Matlab. The proposed computerized methodology focuses student motivation on the mechanical aspects of the problem. Design examples presented illustrate the effectiveness of the approach that provides a solution quality comparable to that of the recently proposed intelligent optimization methods with simplicity of implementation and fast convergence.

Two pages graph layout via recurrent multivalued neural networks

In this work, we propose the use of two neural models performing jointly in order to minimize the same energy function. This model is focused on obtaining good solutions for the two pages book crossing problem, although some others problems can be efficiently solved by the same model. The neural technique applied to this problem allows to reduce the energy function by changing outputs from both networks -outputs of first network representing location of nodes in the nodes line, while the outputs of the second one meaning the half-plane where the edges are drawn. Detailed description of the model is presented, and the technique to minimize an energy function is fully described. It has proved to be a very competitive and efficient algorithm, in terms of quality of solutions and computational time, when compared to the state-of-the-art methods. Some simulation results are presented in this paper, to show the comparative efficiency of the methods.

Theoretical Study on the Capacity of Associative Memory with Multiple Reference Points

An extension to Hopfields model of associative memory is studied in the present work. In particular, this paper is focused in giving solutions to the two main problems present in the model: the apparition of spurious patterns in the learning phase (implying the well-known and undesirable effect of storing the opposite pattern) and the problem of its reduced capacity (the probability of error in the retrieving phase increases as the number of stored patterns grows). In this work, a method to avoid spurious patterns is presented and studied, and an explanation to the previously mentioned effect is given. Another novel technique to increase the capacity of a network is proposed here, based on the idea of using several reference points when storing patterns. It is studied in depth, and an explicit formula for the capacity of the network is provided. This formula shows the linear dependence of the capacity of the new model on the number of reference points, implying the increase of the capacity in this model.