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abstract: The extent of students’ struggles in linear algebra courses is at times surprising to mathematicians and instructors. To gain insight into the challenges, the central question I investigated for this project was: What is the nature of undergraduate students’ conceptions of multiple analytic representations of systems (of equations)? My methodological choices for this study included the use of one-on-one, task-based clinical interviews which were video and audio recorded. Participants were chosen on the basis of selection criteria applied to a pool of volunteers from junior-level applied linear algebra classes. I conducted both generative and convergent analyses in terms of Clement’s (2000) continuum of research purposes. The generative analysis involved an exploration of the data (in transcript form). The convergent analysis involved the analysis of two student interviews through the lenses of Duval’s (1997, 2006, 2017) Theory of Semiotic Representation Registers and a theory I propose, the Theory of Quantitative Systems. All participants concluded that for the four representations in this study, the notation was varying while the solution was invariant. Their descriptions of what was represented by the various representations fell into distinct categories. Further, the students employed visual techniques, heuristics, metaphors, and mathematical computation to account for translations between the various representations. Theoretically, I lay out some constructs that may help with awareness of the complexity in linear algebra. While there are many rich concepts in linear algebra, challenges may stem from less-than-robust communication. Further, mathematics at the level of linear algebra requires a much broader perspective than that of the ordinary algebra of real numbers. Empirically, my results and findings provide important insights into students’ conceptions. The study revealed that students consider and/or can have their interest piqued by such things as changes in register. The lens I propose along with the empirical findings should stimulate conversations that result in linear algebra courses most beneficial to students. This is especially important since students who encounter undue difficulties may alter their intended plans of study, plans which would lead them into careers in STEM (Science, Technology, Engineering, & Mathematics) fields. / Dissertation/Thesis / Doctoral Dissertation Mathematics 2019

<p>Many kernel matrices from differential equations or data science applications possess low or approximately low off-diagonal rank for certain key matrix subblocks; such matrices are referred to as rank-structured. Operations on rank-structured matrices like factorization and linear system solution can be greatly accelerated by converting them into hierarchical matrix forms, such as the hiearchically semiseparable (HSS) matrix form. The dominant cost of this conversion process, called HSS construction, is the low-rank approximation of certain matrix blocks. Low-rank approximation is also a required step in many other contexts throughout numerical linear algebra. In this work, a proxy point low-rank approximation method is detailed for general analytic kernel matrices, in both one and several dimensions. A new accuracy analysis for this approximation is also provided, as well as numerical evidence of its accuracy. The extension of this method to kernels in several dimensions is novel, and its new accuracy analysis makes it a convenient choice to use over existing proxy point methods. Finally, a new HSS construction algorithm using this method for certain Cauchy and Toeplitz matrices is given, which is asymptotically faster than existing methods. Numerical evidence for the accuracy and efficacy of the new construction algorithm is also provided.</p>

<p>This theses is dedicated to the study of generalized diagonal dominance and its<br />various beneflts. The starting point is the well known nonsingularity result of strictly diagonally dominant matrices, from which generalizations were formed in difierent directions. In theses, after a short overview of very well known results, special attention was turned to contemporary contributions, where overview of already published original material is given, together with new obtained results. Particulary, Ger&bull;sgorin-type localization theory for matrix pencils is developed, and application of the results in wireless sensor networks optimization problems is shown.</p> / <p><span class="fontstyle0">Ova teza je posvećena izučavanju generalizovane dijagonalne dominacije i njenih brojnih prednosti. Osnovu čini poznati rezultat o regularnosti strogo dijagonalnih matrica,<br />čija su uop&scaron;tenja formirana u brojnim pravcima. U tezi, nakon kratkog pregleda dobro poznatih rezultata, posebna pažnja je posvećena savremenim doprinosima, gde je dat i pregled već objavljenih autorovih rezultata, kao i detaljan tretman novih dobijenih rezultata. Posebno je razvijena teorija lokalizacije Ger&scaron;gorinovog tipa generalizovanih karakterističnih korena i pokazana je primena rezultata u problemima optimizacije bežičnih senzor mreža.</span></p>

A paramount question in the study of Calcium (Ca2+) signaling is how this ion regulates a wide spectrum of cellular processes, which include: fertilization, proliferation, learning, memory, and cell death. All of these processes are the result of synaptic strengthening and weakening. Part of the answer lies in the spatial-temporal interactions of Ca2+ at the extracellular and intracellular levels of a neuron. Within these levels of a neuron there is a complex concert of Ca2+ ion exchange and transport mechanisms that are activated (or inactivated) by external stimuli and it remains to be studied the role of these interactions at the ultrastructural scale. One mode of external stimulation is by Transcranial Magnetic Stimulation (TMS) and repetitive TMS (rTMS). TMS is a noninvasive brain stimulation method to modulate humanbrain activity by generating a strong magnetic field near the cranium. The magnetic field induces an electric field which depolarizes neurons; therefore, TMS is used in clinical applications to treat neuropsychiatric and neurological disorders. However, it is not well known the effect of TMS on intracellular Ca2+ interactions; therefore, I endeavor to determine the types of calcium interactions that occur when a neuron experiences TMS. I also determine how intracellular calcium mechanisms are affected by TMS stimuli. In particular, the cellular regulators of calcium are given by: the internal Ca2+ store (“calcium bank”) of a neuron called the endoplasmic reticulum (ER) with spine apparatus (SA), the voltage dependent calcium channels (VDCCs), and calcium influx at synaptic spines. Ultimately, the ER is responsible for synaptic plasticity and from here I determined under what conditions does TMS cause intracellular calcium to induce synaptic plasticity. For the first part of this dissertation I describe the neurobiology, model equations, and methods that are employed in understanding the role of intracellular calcium. Simulating calcium dynamics at the ultrastructural level is computationally expensive when including the effects of TMS in concert with intracellular calcium transport mechanism. Therefore, I also identify the numerical methodologies that provide the best results in terms of numerical accuracy to the physiology of the intracellullar dynamics and the parameters such as error and time step size that yield sufficient results. I will also describe the framework used in this study (i.e., UG4) and the pipeline for performing my studies, this includes: the process from microscopy to computational domains, generating and preserving mesh features, the choice of numerical methods, and the process of parallelizing the simulations. In the second part, I dive into the electro-dynamic mechanisms that cause voltage propagation through a neuron. This is of particular importance, because many ion membrane transport mechanisms depend on plasma membrane voltage. The simulations coded and executed in MatLab are used to drive calcium dynamics which is discussed in the third part of the dissertation. I will also take the opportunity to explain a case study involving virtual reality with the Hodgkin-Huxley electrical model for voltage propagation. Additionally, I incorporate synaptic communication which is driven by TMS protocols or simulated by voltage clamps, and both provide a mechanism by which intracellular calcium transients occurs. For the third chapter I discuss the calcium dynamic mechanisms that are inside of neurons and I discuss the methodology I take to setup a simulation and perform simulations. This includes the steps taken to process microscopy images to generate computational domains, implementing the model equations, and utilizing appropriate numerical schemes. I also discuss several preliminary examples as proof of concept to my simulation pipeline and I give results involving the regulation of calcium with respect to intracellular mechanisms. The fourth part of this dissertation describes the steps for running TMS simulations using voltage data from electrical simulations to drive calcium signaling events. In particular, I discuss the tool NeMo-TMS which uses voltage and calcium simulations together to draw conclusions with respect to intracellular calcium propagation. I describe the multi-scale paradigm that is used, model equations, and computational domains that are used and provide several examples of results from this modeling pipeline. Of particular importance, I provide discussion on the coupling of data from electrical simulations and biochemical simulations, i.e. I use TMS induced voltage data to drive voltage dependent calcium release and I examine the effects of TMS induced back propagating action potentials. / Mathematics

This thesis describes an efficient method for speeding up functional verification of arithmetic circuits namely linear network such as wallace trees, counters using linear algebra techniques. The circuit is represented as a network of half adders, full adders and inverters, and modeled as a system of linear equations. The proof of functional correctness of the design is obtained by computing its algebraic signature using standard linear programming (LP) solver and comparing it with the reference signature provided by the designer. Initial experimental results and comparison with Satisfiability Modulo Theorem (SMT) solvers show that the method is efficient, scalable and applicable to complex arithmetic designs, including large multipliers. It is intended to provide a new front end theory/engine to enhance SMT solvers.

Visualization of three-dimensional vector operations can be very helpful in understanding vector mathematics. However, creating these visualizations using traditional WIMP interfaces can be a troublesome exercise. In this thesis, we present VectorPad, a pen-based application for three-dimensional vector mathematics visualization. VectorPad allows users to define vectors and perform mathematical operations upon them through the recognition of handwritten mathematics. The VectorPad user interface consists of a sketching area, where the user can write vector definitions and other mathematics, and a 3D graph for visualization. After recognition, vectors are visualized dynamically on the graph, which can be manipulated by the user. A variety of mathematical operations can be performed, such as addition, subtraction, scalar multiplication, and cross product. Animations show how operations work on the vectors. We also performed a short, informal user study evaluating the user interface and visualizations of VectorPad. VectorPad's visualizations were generally well liked; results from the study show a need to provide a more comprehensive set of visualization tools as well as refinement to some of the animations.

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