Computer Assistance for Discovering\u27\u27 Formulas in System Engineering and Operator Theory

The objective of this paper is two-fold. First we present a methodology for using a combination of computer assistance and human intervention to discover highly algebraic theorems in operator, matrix, and linear systems engineering theory. Since the methodology allows limited human intervention, it is slightly less rigid than an algorithm. We call it a strategy. The second objective is to illustrate the methodology by deriving four theorems. The presentation of the methodology is carried out in three steps. The first step is introducing an abstraction of the methodology which we call an idealized strategy. This abstraction facilitates a high level discussion of the ideas involved. Idealized strategies cannot be implemented on a computer. The second and third steps introduce approximations of these abstractions which we call prestrategy and strategy, respectively. A strategy is more general than a prestrategy and, in fact, every prestrategy is a strategy. The above mentioned approximations are implemented on a computer. We stress that, since there is a computer implementation, the reader can usethese techniques to attack their own algebra problems. Thus the paper might be of both practical and theoretical interest to analysts, engineers, and algebraists. Now we give the idea of a prestrategy. A prestrategy relies almost entirely on two commands which we call NCProcess1 and NCProcess2. These two commands are sufficiently powerful so that, in many cases, when one applies them repeatedly to a complicated collection of equations, they transform the collection of equations into an equivalent but substantially simpler collection of equations. A loose description of a prestrategy applied to a list of equations is: (1) Declare which variables are known and which are unknown. At the beginning of a prestrategy, the order in which the equations are listed is not important, since NCProcess1 and NCProcess2 will reorder them so that the simplest ones appear first. (2) Apply NCProcess1 to the equations; the output is a set of equations, usually some in fewer unknowns than before, carefully partitioned based upon which unknowns they contain. (3) The user must select “important equations,” especially any which solve for an unknown, say x. (When an equation is declared to be important or a variable is switched from being an unknown to being a known, then the way in which NCProcess1 and NCProcess2 reorder the equations is modified.) (4) Switch x to being known rather than unknown. Go to (2) above or stop. When this procedure stops, it hopefully gives the “canonical” necessary conditions for the original equations to have a solution. As a final step we run NCProcess2 which aggressively eliminates redundant equations and partitions the output equations in a way which facilitates proving that the necessary conditions are also sufficient. Many classical theorems in analysis can be viewed in terms of solving a collection of equations. We have found that this procedure actually discovers the classic theorem in a modest collection of classic cases involving factorization of engineering systems and matrix completion problems. One might regard the question of which classical theorems in analysis can be proven with a strategy as an analog of classical Euclidean geometry where a major question was what can be constructed with a compass and ruler. Here the goal is to determine which theorems in systems and operator theory could be discovered by repeatedly applying NCProcess1 and NCProcess2 (or their successors) and the (human) selection of equations which are important. The major practical challenge addressed here is finding operations which, when implemented in software, present the user with crucial algebraic information about his problem while not overwhelming him with too much redundant information. This paper consists of two parts. A description of strategies, a high-level description of the algorithms, a description of the applications to operator, matrix, and linear system engineering theory, and a description of how one would use a strategy to “discover” four different theorems are presented in the first part of the paper. Thus, one who seeks a conventional viewpoint for this rather unconventional paper might think of this as providing a unified proof of four different theorems. The theorems were selected for their diverse proofs and because they are widely known (so that many readers should be familiar with at least one of them). The NCProcess commands use noncommutative Gröbner Basis algorithms which have emerged in the last decade, together with algorithms for removing redundant equations and a method for assisting a mathematician in writing a (noncommutative) polynomial as a composition of polynomials. The reader needs to know nothing about Gröbner Basis to understand the first part of this paper. Descriptions involving the theory of Gröbner Basis appear in the second part of the paper

Computer Assistance In Discovering Formulas And Theorems In System Engineering II

[HSWcdc94] focused on procedures for simplifying complicated expressions automatically. [HScdc95] turned to the adventurous pursuit of developing a highly computer assisted method for “discovering” certain types of formulas and theorems. It is often the case that some variables in the formulation of a problem are not the natural “coordinates” for solution of the problem. Gröbner Basis Algorithms, which lie at the core of our method, are very good at eliminating unknowns, but have no way of finding good changes of variables. This paper gives a way of incorporating changes of variables into our method. As an example, we “discover” the DGKF equations of H∞ control

Noncommutative Computer Algebra in the Control of Singularly Perturbed Dynamical Systems

Most algebraic calculations which one sees in linear systems theory, for example in IEEE TAC, involve block matrices and so are highly noncommutative. Thus conventional commutative computer algebra packages, as in Mathematica and Maple, do not address them. Here we investigate the usefulness of noncommutative computer algebra in a particular area of control theory-singularly perturbed dynamic systems-where working with the noncommutative polynomials involved is especially tedious. Our conclusion is that they have considerable potential for helping practitioners with such computations. For example, the methods introduced here take the most standard textbook singular perturbation calculation, [KK086], one step further than had been done previously. Commutative Groebner basis algorithms are powerful and make up the engines in symbolic algebra packages’ Solve commands. Noncommutative Groebner basis algorithms are more recent, but we shall see that they are useful in manipulating the messy sets of noncommutative polynomial equations which arise in singular perturbation calculations. We use the noncommutative algebra package NCAlgebra and the noncommutative Groebner basis package NCGB which runs under it

Beyond the Fermi Liquid Paradigm: Hidden Fermi Liquids

An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely high temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this "perspective" article is to note that they subscribe to a common underlying paradigm: they both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests.Comment: perspective articl

Developing an Injury Severity to Yield Loss Relationship for Soybean Gall Midge (Diptera: Cecidomyiidae)

Soybean gall midge, Resseliella maxima Gagné (Diptera: Cecidomyiidae), is a newly identified pest confirmed on soybean, Glycine max (L.) Merr. (Fabales: Fabaceae). To date, soybean gall midge has been found in Nebraska, Iowa, South Dakota, Minnesota, and Missouri, and has caused severe economic loss to commercial fields since 2018. Much is still unknown about this pest, so research efforts have been focused on biology and management. Larvae feed on the inside of the stem just above the soil line and are difficult to access and time-consuming to sample. In order to accelerate nondestructive sampling efforts, we developed an injury rating system to quantify the severity of plant injury from soybean gall midge larvae. Research plots from 2019 and 2020 in Iowa and Nebraska were evaluated for injury throughout the growing season and yield was measured. Our objective was to describe the relationship between injury severity and yield loss caused from soybean gall midge. A nonlinear regression model was developed to validate our injury rating system and to express the relationship between season long injury severity and yield loss. Results from our analysis indicate the injury rating system we developed correlates well with yield loss caused by larvae and may be an important tool for understanding the economic impact of this emergent pest of soybeans

Effects of Cognitive Fatigue on High Intensity Circuit Exercise: Preliminary study

Please refer to the pdf version of the abstract located adjacent to the title

Dzyaloshinskii-Moriya interaction and spin re-orientation transition in the frustrated kagome lattice antiferromagnet

Magnetization, specific heat, and neutron scattering measurements were performed to study a magnetic transition in jarosite, a spin-5/2 kagome lattice antiferromagnet. When a magnetic field is applied perpendicular to the kagome plane, magnetizations in the ordered state show a sudden increase at a critical field H_c, indicative of the transition from antiferromagnetic to ferromagnetic states. This sudden increase arises as the spins on alternate kagome planes rotate 180 degrees to ferromagnetically align the canted moments along the field direction. The canted moment on a single kagome plane is a result of the Dzyaloshinskii-Moriya interaction. For H < H_c, the weak ferromagnetic interlayer coupling forces the spins to align in such an arrangement that the canted components on any two adjacent layers are equal and opposite, yielding a zero net magnetic moment. For H > H_c, the Zeeman energy overcomes the interlayer coupling causing the spins on the alternate layers to rotate, aligning the canted moments along the field direction. Neutron scattering measurements provide the first direct evidence of this 180-degree spin rotation at the transition.Comment: 13 pages, 15 figure