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Purpose - The purpose of this paper is to improve the existing differential evolution (DE) mutation operator so as to accelerate its convergence.Design methodology approach - A new general donor form for mutation operation in DE is presented, which defines a donor as a convex combination of the triplet of individuals selected for a mutation. Three new donor schemes from that form are deduced.Findings - The three donor schemes were empirically compared with the original DE version and three existing variants of DE by using a suite of nine well-known test functions, and were also demonstrated by a practical application case - training a neural network to approximate aerodynamic data. The obtained numerical simulation results suggested that these modifications to the mutation operator could improve the DE's convergence performance in both the convergence rate and the convergence reliability.Research limitations implications - Further research is still needed for adequately explaining why it was possible to simultaneously improve both the convergence rate and the convergence reliability of DE to that extent despite the well-known \"No Free Lunch\" theorem. Also further research is considered necessary for outlining more distinctively the particular class of problems, where the current observations can be generalized.Practical implications - More complicated engineering problems could be solved sub-optimally, whereas their real optimal solution may never be reached subject to the current computer capability.Originality value - Though DE has demonstrated a considerably better convergence performance than the other evolutionary algorithms (EAs), its convergence rate is still far from what is hoped for by scientists. On the one hand, a higher convergence rate is always expected for any optimization method used in seeking the global optimum of a non-linear objective function. On the other hand, since all EAs, including DE, work with a population of solutions rather than a single solution, many evaluations of candidate solutions are required in the optimization process. If evaluation of candidate solutions is too time-consuming, the overall optimization cost may become too expensive. One often has to limit the algorithm to operate within an acceptable time, which maybe is not enough to find the global optimum (optima), but enough to obtain a sub-optimal solution. Therefore, it is continuously necessary to investigate the new strategies to improve the current DE algorithm.

Algorithm design courses are fundamental to computer science curricula, but fostering algorithmic thinking in students is challenging due to the diverse skills and creativity required. Dedicated teaching support tools can help both course instructors and students in this effort. We have developed the Alk platform to promote algorithmic thinking, leveraging the theoretical foundations of Matching Logic. Alk features an intuitive algorithm language that provides a flexible computational model suitable for analysis, symbolic execution, and checking properties of algorithms. In this paper, we present an overview of the Alk platform tool and demonstrate, through use cases, how it fosters various algorithmic thinking skills. We conclude that the Alk platform is a valuable tool for learning and teaching algorithms, effectively enhancing students' understanding and skills. Future work will extend its capabilities of supporting symbolic execution, probabilistic algorithms, as well as estimation of execution time, further broadening its impact on computer science education.

Purpose This paper aims to provide a more rapid stress updating algorithm for vonMises plasticity with mixedhardening and to compare it with the previous works. Designmethodologyapproach An augmented stress vector is defined. This can convert the original nonlinear differential equation system to a quasilinear one. Then the dynamical system can be solved with an exponential map approach in a semiimplicit manner. Findings The presented stress updating algorithm gives very accurate results and it has a quadratic convergence rate. Research limitationsimplications VonMises plasticity in a small strain regime is considered. Furthermore, the material is supposed to have linear hardening. Practical implications Stress updating is the heart of a nonlinear finite element analysis due to the large consumption of computation time. The efficiency and accuracy of the calculations of nonlinear finite element analysis are strongly influenced by the efficiency and accuracy of stress updating schemes. Originalityvalue The paper offers a new stress updating strategy based on exponential maps. This may be used as a routine in a nonlinear finite element analysis software to enhance its performance.

Purpose The purpose of this paper is to propose to overcome the limitations of polygonization of point clouds for rapid prototyping purposes, by using a direct slicing approach, based on a hybrid localgenetic algorithm to achieve a robust direct slicing system. Designmethodologyapproach At first a volume analysis is performed on the point cloud and a space decomposition is realized using elementary voxels. Then, considering each Z level of the voxelized point cloud, the external nonvoid voxels are linked togheter using an hybrid local and genetic approach, to generate the contour of the object with an automatic process. The contour of the object is finally converted into slice files suitable for the rapid prototyping machine. Findings The genetic algorithm GA is very effective in detecting those slices where an optimal solution is not achieved with the local approach, and in finding the minimum path that connects the points belonging to the slice contour. Research limitationsimplications Further studies must be conducted to improve the efficiency of the approach to the travelling salesman problem TSP and to the relation between the cell dimension and the point cloud density. In this context, the use of adaptive slicing will be considered, in order to improve time performances. Practical implications The approach is fully automated and enables the direct creation of layered manufactured copies of 3D scanned products directly from the point clouds, avoiding the tessellation phase that is often time consuming and characterized by errors in the STL file. Originalityvalue The use of TSP problem to solve the direct slicing of point clouds is more effective than simple spline fitting techniques, avoiding selfcrossing curves. This approach solves the TSP problem for each slice, exploiting the volumetric space decomposition to fasten the achievement of the solution. In fact the local knowledge is used by the nearest neighbours local search and the partial solution achieved is the starting point of the GA. The GA is effective in finding global minima and results to be fastened by the local approach.

Purpose The main purpose of this paper is to compare the performance of three commonly used global search algorithms, namely treebased augmented spatial digital tree, cellbased no binary search and Dcell, in the discrete element simulations. Designmethodologyapproach A large number of test cases with up to five million particlesdiscrete objects are employed to numerically examine the computational costs of the three search algorithms and their performance is compared. Findings Comprehensive comparisons reveal that the Dcell is more efficient than the treebased search algorithms for largescale problems. The parametric study of the Dcell algorithm itself shows that the performance of the algorithm is strongly dependent on the cell dimension chosen. Research limitationsimplications The only limitation of the current work is that the tested domain shape is regular, and thus more complex domain shapes may need to be considered. Originalityvalue The paper provides clear guidance regarding the possible actual computational performance of the tested search algorithms for practical applications.

Pupose The purpose of this paper is to show that a fingerprinting code is a set of code words that are embedded in each copy of a digital object, with the purpose of making each copy unique. If the fingerprinting code is csecure, then the decoding of a pirate word created by a coalition of at most c dishonest users, will expose at least one of the guilty parties. Designmethodologyapproach The paper presents a systematic strategy for collusions attacking a fingerprinting scheme. As a particular case, this strategy shows that linear codes are not good fingerprinting codes. Based on binary linear equidistant codes, the paper constructs a family of fingerprinting codes in which the identification of guilty users can be efficiently done using minimum distance decoding. Moreover, in order to obtain codes with a better rate a 2secure fingerprinting code is also constructed by concatenating a code from the previous family with an outer IPP code. Findings The particular choice of the codes is such that it allows the use of efficient decoding algorithms that correct errors beyond the error correction bound of the code, namely a simplified version of the Chase algorithms for the inner code and the KoetterVardy softdecision list decoding algorithm for the outer code. Originalityvalue The paper presents a fingerprinting code together with an efficient chasing algorithm.

Purpose Stereo vision is an attractive perception technique for mobile robots navigation. Stereo matching is a crucial part of stereo vision and its precision dominates the precision of reconstruction. Based on a geometry constraint applicable to natural terrain, the purpose of this paper is to present a multistage stereo matching algorithm to improve matching accuracy. Designmethodologyapproach In the multistage matching algorithm, points with larger intensity gradient are matched in earlier stages. Using several constraints and statistical means, information from earlier stages is utilized to assist in matching of later stages to improve matching accuracy. Findings The multistage matching algorithm improves the matching accuracy of stereo pairs of natural terrain in various conditions. Research limitationsimplications The algorithm demonstrates advantages over areamatching algorithm both in matching accuracy and computation efficiency. However, if used for realtime navigation, it still needs the assistance of specialized hardware or window selection technique. Practical implications The algorithm is able to produce dense disparity maps of natural terrain with fairly high accuracy and can be used for the navigation of planetary rover or other outdoor mobile robots. Originalityvalue The paper provides a new approach to produce accurate and dense disparity maps of natural terrain, which laid the foundation for its use in outdoor mobile robots navigation.

Purpose The purpose of this paper is to propose efficient algorithms for structural grouping over Extensible Markup Language XML data, called TOPOLOGICAL ROLLUP TROLLUP, which are to compute aggregation functions based on XML data with multiple hierarchical levels. They play important roles in the online analytical processing of XML data, called XMLOLAP, with which complex analysis over XML can be performed to discover valuable information from XML. Designmethodologyapproach Several variations of algorithms are proposed for efficient TROLLUP computation. First, two basic algorithms, topdown algorithm TDA and bottomup algorithm BUA, are presented in which the wellknown structuraljoin algorithms are used. The paper then proposes more efficient algorithms, called singlescan by preorder number and singlescan by postorder number SSCPrePost, which are also based on structural joins, but have been modified from the basic algorithms so that multiple levels of grouping are computed with a single scan over node lists. In addition, the paper attempts to adopt the algorithm for parallel execution in multicore environments. Findings Several experiments are conducted with XMark and synthetic XML data to show the effectiveness of the proposed algorithms. The experiments show that proposed algorithms perform much better than the nave implementation. In particular, the proposed SSCPre and SSCPost perform better than TDA and BUA for all cases. Beyond that, the experiment using the parallel single scan algorithm also shows better performance than the ordinary basic algorithm. Research limitationsimplications This paper focuses on the TROLLUP operation for XML data analysis. For this reason, other operations related to XMLOLAP, such as CUBE, WINDOWING, and RANKING should also be investigated. Originalityvalue The paper presents an extended version of one of the award winning papers at iiWAS2008.

Purpose This paper seeks to examine the development of the onboard guidance law for multirevolutions orbit transfer spacecraft with lowthrust propulsion systems. Designmethodologyapproach In the research, first, a set of equinoctial elements is utilized to avoid the singularities in dynamical equation of classical orbit elements. A thruster switch law is derived by analyzing the efficiency of the changing of each orbit elements. Second, by using the theory of Lyapunov feedback control, analytic expressions of thrust angles are derived. Finally, the weights of the Lyapunov function are adjusted by hybrid genetic algorithm to improve the performance of the guidance law. Findings First, the dynamical equations of classical orbit elements are always singularity during the orbit transfer. By using modified equinoctial elements, these singularities could be avoided. Second, the trajectory is sensitive to the weights in Lyapunov function. With reasonable weights, the key parameters under the control of the guidance law presented in this paper are very close to that of optimal trajectory. Research limitationsimplications In further research, some dynamical weights methods will be used in the control law to improve the performance index, and approach the optimal solution. Practical implications The guidance law presented in this paper could be easily used as an onboard algorithm for the multirevolutions orbit transfer or stationkeeping. Furthermore, it could also be utilized as an initial design method for lowthrust orbit transfer. Originalityvalue Providing a lowthrust guidance law by combining the concept of Lyapunov feedback control with hybrid genetic algorithm. This method has a super convergence and a lowcomputational cost.

Between the genesis of computer science in the 1960s and the advent of the World Wide Web around 1990, computer science evolved in significant ways. The author has termed this period the \"second age of computer science.\" This book describes its evolution in the form of several interconnected parallel histories.