Approximation and Errors
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An Introduction to Mathematical Modelling
An Introduction to Mathematical Modelling Glenn Marion, Bioinformatics and Statistics Scotland Given 2008 by Daniel Lawson and Glenn Marion 2008 Contents 1 Introduction 1 1.1 Whatismathematicalmodelling?. .......... 1 1.2 Whatobjectivescanmodellingachieve? . ............ 1 1.3 Classificationsofmodels . ......... 1 1.4 Stagesofmodelling............................... ....... 2 2 Building models 4 2.1 Gettingstarted .................................. ...... 4 2.2 Systemsanalysis ................................. ...... 4 2.2.1 Makingassumptions ............................. .... 4 2.2.2 Flowdiagrams .................................. 6 2.3 Choosingmathematicalequations. ........... 7 2.3.1 Equationsfromtheliterature . ........ 7 2.3.2 Analogiesfromphysics. ...... 8 2.3.3 Dataexploration ............................... .... 8 2.4 Solvingequations................................ ....... 9 2.4.1 Analytically.................................. .... 9 2.4.2 Numerically................................... 10 3 Studying models 12 3.1 Dimensionlessform............................... ....... 12 3.2 Asymptoticbehaviour ............................. ....... 12 3.3 Sensitivityanalysis . ......... 14 3.4 Modellingmodeloutput . ....... 16 4 Testing models 18 4.1 Testingtheassumptions . ........ 18 4.2 Modelstructure.................................. ...... 18 i 4.3 Predictionofpreviouslyunuseddata . ............ 18 4.3.1 Reasonsforpredictionerrors . ........ 20 4.4 Estimatingmodelparameters . ......... 20 4.5 Comparingtwomodelsforthesamesystem . ......... -
Example 10.8 Testing the Steady-State Approximation. ⊕ a B C C a B C P + → → + → D Dt K K K K K K [ ]
Example 10.8 Testing the steady-state approximation. Å The steady-state approximation contains an apparent contradiction: we set the time derivative of the concentration of some species (a reaction intermediate) equal to zero — implying that it is a constant — and then derive a formula showing how it changes with time. Actually, there is no contradiction since all that is required it that the rate of change of the "steady" species be small compared to the rate of reaction (as measured by the rate of disappearance of the reactant or appearance of the product). But exactly when (in a practical sense) is this approximation appropriate? It is often applied as a matter of convenience and justified ex post facto — that is, if the resulting rate law fits the data then the approximation is considered justified. But as this example demonstrates, such reasoning is dangerous and possible erroneous. We examine the mechanism A + B ¾¾1® C C ¾¾2® A + B (10.12) 3 C® P (Note that the second reaction is the reverse of the first, so we have a reversible second-order reaction followed by an irreversible first-order reaction.) The rate constants are k1 for the forward reaction of the first step, k2 for the reverse of the first step, and k3 for the second step. This mechanism is readily solved for with the steady-state approximation to give d[A] k1k3 = - ke[A][B] with ke = (10.13) dt k2 + k3 (TEXT Eq. (10.38)). With initial concentrations of A and B equal, hence [A] = [B] for all times, this equation integrates to 1 1 = + ket (10.14) [A] A0 where A0 is the initial concentration (equal to 1 in work to follow). -
A Short Course on Approximation Theory
A Short Course on Approximation Theory N. L. Carothers Department of Mathematics and Statistics Bowling Green State University ii Preface These are notes for a topics course offered at Bowling Green State University on a variety of occasions. The course is typically offered during a somewhat abbreviated six week summer session and, consequently, there is a bit less material here than might be associated with a full semester course offered during the academic year. On the other hand, I have tried to make the notes self-contained by adding a number of short appendices and these might well be used to augment the course. The course title, approximation theory, covers a great deal of mathematical territory. In the present context, the focus is primarily on the approximation of real-valued continuous functions by some simpler class of functions, such as algebraic or trigonometric polynomials. Such issues have attracted the attention of thousands of mathematicians for at least two centuries now. We will have occasion to discuss both venerable and contemporary results, whose origins range anywhere from the dawn of time to the day before yesterday. This easily explains my interest in the subject. For me, reading these notes is like leafing through the family photo album: There are old friends, fondly remembered, fresh new faces, not yet familiar, and enough easily recognizable faces to make me feel right at home. The problems we will encounter are easy to state and easy to understand, and yet their solutions should prove intriguing to virtually anyone interested in mathematics. The techniques involved in these solutions entail nearly every topic covered in the standard undergraduate curriculum. -
Differentiation Rules (Differential Calculus)
Differentiation Rules (Differential Calculus) 1. Notation The derivative of a function f with respect to one independent variable (usually x or t) is a function that will be denoted by D f . Note that f (x) and (D f )(x) are the values of these functions at x. 2. Alternate Notations for (D f )(x) d d f (x) d f 0 (1) For functions f in one variable, x, alternate notations are: Dx f (x), dx f (x), dx , dx (x), f (x), f (x). The “(x)” part might be dropped although technically this changes the meaning: f is the name of a function, dy 0 whereas f (x) is the value of it at x. If y = f (x), then Dxy, dx , y , etc. can be used. If the variable t represents time then Dt f can be written f˙. The differential, “d f ”, and the change in f ,“D f ”, are related to the derivative but have special meanings and are never used to indicate ordinary differentiation. dy 0 Historical note: Newton used y,˙ while Leibniz used dx . About a century later Lagrange introduced y and Arbogast introduced the operator notation D. 3. Domains The domain of D f is always a subset of the domain of f . The conventional domain of f , if f (x) is given by an algebraic expression, is all values of x for which the expression is defined and results in a real number. If f has the conventional domain, then D f usually, but not always, has conventional domain. Exceptions are noted below. -
February 2009
How Euler Did It by Ed Sandifer Estimating π February 2009 On Friday, June 7, 1779, Leonhard Euler sent a paper [E705] to the regular twice-weekly meeting of the St. Petersburg Academy. Euler, blind and disillusioned with the corruption of Domaschneff, the President of the Academy, seldom attended the meetings himself, so he sent one of his assistants, Nicolas Fuss, to read the paper to the ten members of the Academy who attended the meeting. The paper bore the cumbersome title "Investigatio quarundam serierum quae ad rationem peripheriae circuli ad diametrum vero proxime definiendam maxime sunt accommodatae" (Investigation of certain series which are designed to approximate the true ratio of the circumference of a circle to its diameter very closely." Up to this point, Euler had shown relatively little interest in the value of π, though he had standardized its notation, using the symbol π to denote the ratio of a circumference to a diameter consistently since 1736, and he found π in a great many places outside circles. In a paper he wrote in 1737, [E74] Euler surveyed the history of calculating the value of π. He mentioned Archimedes, Machin, de Lagny, Leibniz and Sharp. The main result in E74 was to discover a number of arctangent identities along the lines of ! 1 1 1 = 4 arctan " arctan + arctan 4 5 70 99 and to propose using the Taylor series expansion for the arctangent function, which converges fairly rapidly for small values, to approximate π. Euler also spent some time in that paper finding ways to approximate the logarithms of trigonometric functions, important at the time in navigation tables. -
Approximation Atkinson Chapter 4, Dahlquist & Bjork Section 4.5
Approximation Atkinson Chapter 4, Dahlquist & Bjork Section 4.5, Trefethen's book Topics marked with ∗ are not on the exam 1 In approximation theory we want to find a function p(x) that is `close' to another function f(x). We can define closeness using any metric or norm, e.g. Z 2 2 kf(x) − p(x)k2 = (f(x) − p(x)) dx or kf(x) − p(x)k1 = sup jf(x) − p(x)j or Z kf(x) − p(x)k1 = jf(x) − p(x)jdx: In order for these norms to make sense we need to restrict the functions f and p to suitable function spaces. The polynomial approximation problem takes the form: Find a polynomial of degree at most n that minimizes the norm of the error. Naturally we will consider (i) whether a solution exists and is unique, (ii) whether the approximation converges as n ! 1. In our section on approximation (loosely following Atkinson, Chapter 4), we will first focus on approximation in the infinity norm, then in the 2 norm and related norms. 2 Existence for optimal polynomial approximation. Theorem (no reference): For every n ≥ 0 and f 2 C([a; b]) there is a polynomial of degree ≤ n that minimizes kf(x) − p(x)k where k · k is some norm on C([a; b]). Proof: To show that a minimum/minimizer exists, we want to find some compact subset of the set of polynomials of degree ≤ n (which is a finite-dimensional space) and show that the inf over this subset is less than the inf over everything else. -
PLEASANTON UNIFIED SCHOOL DISTRICT Math 8/Algebra I Course Outline Form Course Title
PLEASANTON UNIFIED SCHOOL DISTRICT Math 8/Algebra I Course Outline Form Course Title: Math 8/Algebra I Course Number/CBED Number: Grade Level: 8 Length of Course: 1 year Credit: 10 Meets Graduation Requirements: n/a Required for Graduation: Prerequisite: Math 6/7 or Math 7 Course Description: Main concepts from the CCSS 8th grade content standards include: knowing that there are numbers that are not rational, and approximate them by rational numbers; working with radicals and integer exponents; understanding the connections between proportional relationships, lines, and linear equations; analyzing and solving linear equations and pairs of simultaneous linear equations; defining, evaluating, and comparing functions; using functions to model relationships between quantities; understanding congruence and similarity using physical models, transparencies, or geometry software; understanding and applying the Pythagorean Theorem; investigating patterns of association in bivariate data. Algebra (CCSS Algebra) main concepts include: reason quantitatively and use units to solve problems; create equations that describe numbers or relationships; understanding solving equations as a process of reasoning and explain reasoning; solve equations and inequalities in one variable; solve systems of equations; represent and solve equations and inequalities graphically; extend the properties of exponents to rational exponents; use properties of rational and irrational numbers; analyze and solve linear equations and pairs of simultaneous linear equations; define, -
The Exponential Constant E
The exponential constant e mc-bus-expconstant-2009-1 Introduction The letter e is used in many mathematical calculations to stand for a particular number known as the exponential constant. This leaflet provides information about this important constant, and the related exponential function. The exponential constant The exponential constant is an important mathematical constant and is given the symbol e. Its value is approximately 2.718. It has been found that this value occurs so frequently when mathematics is used to model physical and economic phenomena that it is convenient to write simply e. It is often necessary to work out powers of this constant, such as e2, e3 and so on. Your scientific calculator will be programmed to do this already. You should check that you can use your calculator to do this. Look for a button marked ex, and check that e2 =7.389, and e3 = 20.086 In both cases we have quoted the answer to three decimal places although your calculator will give a more accurate answer than this. You should also check that you can evaluate negative and fractional powers of e such as e1/2 =1.649 and e−2 =0.135 The exponential function If we write y = ex we can calculate the value of y as we vary x. Values obtained in this way can be placed in a table. For example: x −3 −2 −1 01 2 3 y = ex 0.050 0.135 0.368 1 2.718 7.389 20.086 This is a table of values of the exponential function ex. -
Function Approximation Through an Efficient Neural Networks Method
Paper ID #25637 Function Approximation through an Efficient Neural Networks Method Dr. Chaomin Luo, Mississippi State University Dr. Chaomin Luo received his Ph.D. in Department of Electrical and Computer Engineering at Univer- sity of Waterloo, in 2008, his M.Sc. in Engineering Systems and Computing at University of Guelph, Canada, and his B.Eng. in Electrical Engineering from Southeast University, Nanjing, China. He is cur- rently Associate Professor in the Department of Electrical and Computer Engineering, at the Mississippi State University (MSU). He was panelist in the Department of Defense, USA, 2015-2016, 2016-2017 NDSEG Fellowship program and panelist in 2017 NSF GRFP Panelist program. He was the General Co-Chair of 2015 IEEE International Workshop on Computational Intelligence in Smart Technologies, and Journal Special Issues Chair, IEEE 2016 International Conference on Smart Technologies, Cleveland, OH. Currently, he is Associate Editor of International Journal of Robotics and Automation, and Interna- tional Journal of Swarm Intelligence Research. He was the Publicity Chair in 2011 IEEE International Conference on Automation and Logistics. He was on the Conference Committee in 2012 International Conference on Information and Automation and International Symposium on Biomedical Engineering and Publicity Chair in 2012 IEEE International Conference on Automation and Logistics. He was a Chair of IEEE SEM - Computational Intelligence Chapter; a Vice Chair of IEEE SEM- Robotics and Automa- tion and Chair of Education Committee of IEEE SEM. He has extensively published in reputed journal and conference proceedings, such as IEEE Transactions on Neural Networks, IEEE Transactions on SMC, IEEE-ICRA, and IEEE-IROS, etc. His research interests include engineering education, computational intelligence, intelligent systems and control, robotics and autonomous systems, and applied artificial in- telligence and machine learning for autonomous systems. -
1. Antiderivatives for Exponential Functions Recall That for F(X) = Ec⋅X, F ′(X) = C ⋅ Ec⋅X (For Any Constant C)
1. Antiderivatives for exponential functions Recall that for f(x) = ec⋅x, f ′(x) = c ⋅ ec⋅x (for any constant c). That is, ex is its own derivative. So it makes sense that it is its own antiderivative as well! Theorem 1.1 (Antiderivatives of exponential functions). Let f(x) = ec⋅x for some 1 constant c. Then F x ec⋅c D, for any constant D, is an antiderivative of ( ) = c + f(x). 1 c⋅x ′ 1 c⋅x c⋅x Proof. Consider F (x) = c e +D. Then by the chain rule, F (x) = c⋅ c e +0 = e . So F (x) is an antiderivative of f(x). Of course, the theorem does not work for c = 0, but then we would have that f(x) = e0 = 1, which is constant. By the power rule, an antiderivative would be F (x) = x + C for some constant C. 1 2. Antiderivative for f(x) = x We have the power rule for antiderivatives, but it does not work for f(x) = x−1. 1 However, we know that the derivative of ln(x) is x . So it makes sense that the 1 antiderivative of x should be ln(x). Unfortunately, it is not. But it is close. 1 1 Theorem 2.1 (Antiderivative of f(x) = x ). Let f(x) = x . Then the antiderivatives of f(x) are of the form F (x) = ln(SxS) + C. Proof. Notice that ln(x) for x > 0 F (x) = ln(SxS) = . ln(−x) for x < 0 ′ 1 For x > 0, we have [ln(x)] = x . -
A Rational Approximation to the Logarithm
A Rational Approximation to the Logarithm By R. P. Kelisky and T. J. Rivlin We shall use the r-method of Lanczos to obtain rational approximations to the logarithm which converge in the entire complex plane slit along the nonpositive real axis, uniformly in certain closed regions in the slit plane. We also provide error esti- mates valid in these regions. 1. Suppose z is a complex number, and s(l, z) denotes the closed line segment joining 1 and z. Let y be a positive real number, y ¿¿ 1. As a polynomial approxima- tion, of degree n, to log x on s(l, y) we propose p* G Pn, Pn being the set of poly- nomials with real coefficients of degree at most n, which minimizes ||xp'(x) — X|J===== max \xp'(x) — 1\ *e«(l.v) among all p G Pn which satisfy p(l) = 0. (This procedure is suggested by the observation that w = log x satisfies xto'(x) — 1=0, to(l) = 0.) We determine p* as follows. Suppose p(x) = a0 + aix + ■• • + a„xn, p(l) = 0 and (1) xp'(x) - 1 = x(x) = b0 + bix +-h bnxn . Then (2) 6o = -1 , (3) a,- = bj/j, j = 1, ■•-,«, and n (4) a0= - E Oj • .-i Thus, minimizing \\xp' — 1|| subject to p(l) = 0 is equivalent to minimizing ||«-|| among all i£P„ which satisfy —ir(0) = 1. This, in turn, is equivalent to maximiz- ing |7r(0) I among all v G Pn which satisfy ||ir|| = 1, in the sense that if vo maximizes |7r(0)[ subject to ||x|| = 1, then** = —iro/-7ro(0) minimizes ||x|| subject to —ir(0) = 1. -
Antiderivatives Math 121 Calculus II D Joyce, Spring 2013
Antiderivatives Math 121 Calculus II D Joyce, Spring 2013 Antiderivatives and the constant of integration. We'll start out this semester talking about antiderivatives. If the derivative of a function F isf, that is, F 0 = f, then we say F is an antiderivative of f. Of course, antiderivatives are important in solving problems when you know a derivative but not the function, but we'll soon see that lots of questions involving areas, volumes, and other things also come down to finding antiderivatives. That connection we'll see soon when we study the Fundamental Theorem of Calculus (FTC). For now, we'll just stick to the basic concept of antiderivatives. We can find antiderivatives of polynomials pretty easily. Suppose that we want to find an antiderivative F (x) of the polynomial f(x) = 4x3 + 5x2 − 3x + 8: We can find one by finding an antiderivative of each term and adding the results together. Since the derivative of x4 is 4x3, therefore an antiderivative of 4x3 is x4. It's not much harder to find an antiderivative of 5x2. Since the derivative of x3 is 3x2, an antiderivative of 5x2 is 5 3 3 x . Continue on and soon you see that an antiderivative of f(x) is 4 5 3 3 2 F (x) = x + 3 x − 2 x + 8x: There are, however, other antiderivatives of f(x). Since the derivative of a constant is 0, 4 5 3 3 2 we can add any constant to F (x) to find another antiderivative. Thus, x + 3 x − 2 x +8x+7 4 5 3 3 2 is another antiderivative of f(x).