108 research outputs found
The Improved Hybrid Algorithm for the Atheer and Berry-Ravindran Algorithms
Exact String matching considers is one of the important ways in solving the basic problems in computer science. This research proposed a hybrid exact string matching algorithm called E-Atheer. This algorithm depended on good features; searching and shifting techniques in the Atheer and Berry-Ravindran algorithms, respectively. The proposed algorithm showed better performance in number of attempts and character comparisons compared to the original and recent and standard algorithms. E-Atheer algorithm used several types of databases, which are DNA, Protein, XML, Pitch, English, and Source. The best performancein the number of attempts is when the algorithm is executed using the pitch dataset. The worst performance is when it is used with DNA dataset. The best and worst databases in the number of character comparisons with the E-Atheer algorithm are the Source and DNA databases, respectively
On the Comparison Complexity of the String Prefix-Matching Problem
In this paper we study the exact comparison complexity of the stringprefix-matching problem in the deterministic sequential comparison modelwith equality tests. We derive almost tight lower and upper bounds onthe number of symbol comparisons required in the worst case by on-lineprefix-matching algorithms for any fixed pattern and variable text. Unlikeprevious results on the comparison complexity of string-matching andprefix-matching algorithms, our bounds are almost tight for any particular pattern.We also consider the special case where the pattern and the text are thesame string. This problem, which we call the string self-prefix problem, issimilar to the pattern preprocessing step of the Knuth-Morris-Pratt string-matchingalgorithm that is used in several comparison efficient string-matchingand prefix-matching algorithms, including in our new algorithm.We obtain roughly tight lower and upper bounds on the number of symbolcomparisons required in the worst case by on-line self-prefix algorithms.Our algorithms can be implemented in linear time and space in thestandard uniform-cost random-access-machine model
Learning to sample in Cartesian MRI
Despite its exceptional soft tissue contrast, Magnetic Resonance Imaging
(MRI) faces the challenge of long scanning times compared to other modalities
like X-ray radiography. Shortening scanning times is crucial in clinical
settings, as it increases patient comfort, decreases examination costs and
improves throughput. Recent advances in compressed sensing (CS) and deep
learning allow accelerated MRI acquisition by reconstructing high-quality
images from undersampled data. While reconstruction algorithms have received
most of the focus, designing acquisition trajectories to optimize
reconstruction quality remains an open question. This thesis explores two
approaches to address this gap in the context of Cartesian MRI. First, we
propose two algorithms, lazy LBCS and stochastic LBCS, that significantly
improve upon G\"ozc\"u et al.'s greedy learning-based CS (LBCS) approach. These
algorithms scale to large, clinically relevant scenarios like multi-coil 3D MR
and dynamic MRI, previously inaccessible to LBCS. Additionally, we demonstrate
that generative adversarial networks (GANs) can serve as a natural criterion
for adaptive sampling by leveraging variance in the measurement domain to guide
acquisition. Second, we delve into the underlying structures or assumptions
that enable mask design algorithms to perform well in practice. Our experiments
reveal that state-of-the-art deep reinforcement learning (RL) approaches, while
capable of adaptation and long-horizon planning, offer only marginal
improvements over stochastic LBCS, which is neither adaptive nor does long-term
planning. Altogether, our findings suggest that stochastic LBCS and similar
methods represent promising alternatives to deep RL. They shine in particular
by their scalability and computational efficiency and could be key in the
deployment of optimized acquisition trajectories in Cartesian MRI.Comment: PhD Thesis; 198 page
Efficient string algorithmics across alphabet realms
Stringology is a subfield of computer science dedicated to analyzing and processing sequences of symbols. It plays a crucial role in various applications, including lossless compression, information retrieval, natural language processing, and bioinformatics. Recent algorithms often assume that the strings to be processed are over polynomial integer alphabet, i.e., each symbol is an integer that is at most polynomial in the lengths of the strings. In contrast to that, the earlier days of stringology were shaped by the weaker comparison model, in which strings can only be accessed by mere equality comparisons of symbols, or (if the symbols are totally ordered) order comparisons of symbols. Nowadays, these flavors of the comparison model are respectively referred to as general unordered alphabet and general ordered alphabet. In this dissertation, we dive into the realm of both integer alphabets and general alphabets. We present new algorithms and lower bounds for classic problems, including Lempel-Ziv compression, computing the Lyndon array, and the detection of squares and runs. Our results show that, instead of only assuming the standard model of computation, it is important to also consider both weaker and stronger models. Particularly, we should not discard the older and weaker comparison-based models too quickly, as they are not only powerful theoretical tools, but also lead to fast and elegant practical solutions, even by today's standards
Connected Attribute Filtering Based on Contour Smoothness
A new attribute measuring the contour smoothness of 2-D objects is presented in the context of morphological attribute filtering. The attribute is based on the ratio of the circularity and non-compactness, and has a maximum of 1 for a perfect circle. It decreases as the object boundary becomes irregular. Computation on hierarchical image representation structures relies on five auxiliary data members and is rapid. Contour smoothness is a suitable descriptor for detecting and discriminating man-made structures from other image features. An example is demonstrated on a very-high-resolution satellite image using connected pattern spectra and the switchboard platform
QAmplifyNet: Pushing the Boundaries of Supply Chain Backorder Prediction Using Interpretable Hybrid Quantum - Classical Neural Network
Supply chain management relies on accurate backorder prediction for
optimizing inventory control, reducing costs, and enhancing customer
satisfaction. However, traditional machine-learning models struggle with
large-scale datasets and complex relationships, hindering real-world data
collection. This research introduces a novel methodological framework for
supply chain backorder prediction, addressing the challenge of handling large
datasets. Our proposed model, QAmplifyNet, employs quantum-inspired techniques
within a quantum-classical neural network to predict backorders effectively on
short and imbalanced datasets. Experimental evaluations on a benchmark dataset
demonstrate QAmplifyNet's superiority over classical models, quantum ensembles,
quantum neural networks, and deep reinforcement learning. Its proficiency in
handling short, imbalanced datasets makes it an ideal solution for supply chain
management. To enhance model interpretability, we use Explainable Artificial
Intelligence techniques. Practical implications include improved inventory
control, reduced backorders, and enhanced operational efficiency. QAmplifyNet
seamlessly integrates into real-world supply chain management systems, enabling
proactive decision-making and efficient resource allocation. Future work
involves exploring additional quantum-inspired techniques, expanding the
dataset, and investigating other supply chain applications. This research
unlocks the potential of quantum computing in supply chain optimization and
paves the way for further exploration of quantum-inspired machine learning
models in supply chain management. Our framework and QAmplifyNet model offer a
breakthrough approach to supply chain backorder prediction, providing superior
performance and opening new avenues for leveraging quantum-inspired techniques
in supply chain management
Dynamics of retinotopic spatial attention revealed by multifocal MEG
Visual focal attention is both fast and spatially localized, making it challenging to investigate using human neu-roimaging paradigms. Here, we used a new multivariate multifocal mapping method with magnetoencephalog-raphy (MEG) to study how focal attention in visual space changes stimulus-evoked responses across the visual field. The observer's task was to detect a color change in the target location, or at the central fixation. Simulta-neously, 24 regions in visual space were stimulated in parallel using an orthogonal, multifocal mapping stimulus sequence. First, we used univariate analysis to estimate stimulus-evoked responses in each channel. Then we applied multivariate pattern analysis to look for attentional effects on the responses. We found that attention to a target location causes two spatially and temporally separate effects. Initially, attentional modulation is brief, observed at around 60-130 ms post stimulus, and modulates responses not only at the target location but also in adjacent regions. A later modulation was observed from around 200 ms, which was specific to the location of the attentional target. The results support the idea that focal attention employs several processing stages and suggest that early attentional modulation is less spatially specific than late.Peer reviewe
Dimensionality reduction beyond neural subspaces with slice tensor component analysis
Recent work has argued that large-scale neural recordings are often well described by patterns of coactivation across neurons. Yet the view that neural variability is constrained to a fixed, low-dimensional subspace may overlook higher-dimensional structure, including stereotyped neural sequences or slowly evolving latent spaces. Here we argue that task-relevant variability in neural data can also cofluctuate over trials or time, defining distinct ‘covariability classes’ that may co-occur within the same dataset. To demix these covariability classes, we develop sliceTCA (slice tensor component analysis), a new unsupervised dimensionality reduction method for neural data tensors. In three example datasets, including motor cortical activity during a classic reaching task in primates and recent multiregion recordings in mice, we show that sliceTCA can capture more task-relevant structure in neural data using fewer components than traditional methods. Overall, our theoretical framework extends the classic view of low-dimensional population activity by incorporating additional classes of latent variables capturing higher-dimensional structure
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