Solving non-linear systems of equations
|
|
- Moris Williams
- 6 years ago
- Views:
Transcription
1 Solving non-linear systems of equations Felix Kubler 1 1 DBF, University of Zurich and Swiss Finance Institute October 7, 2017 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
2 The problem We consider a system of equations f (x) = 0, f : U R n R n We will usually assume that f is C 2 although often/sometimes the methods go through with f being continuous. In the economic applications, we will make assumptions that ensure that there is some x with f ( x) = 0 and with D x f ( x) being invertible. If x satisfies the latter condition, we call the solution locally unique. Sometimes methods work without this, but if Jacobian is ill-conditioned, we re typically in trouble Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
3 Economic application t = 0,..., T. Uncertainty driven by a Markov chain s t {1,..., S} with transition π. Denote by s t a history of shocks (node of the event tree) H agents with utility U h (c) = E 0 T β t u(c t ), Agents have stationary endowments e h (s t ) that depend on the shock, s t. J long lived assets, Lucas trees, that pay dividends d(s t ) 0. It is useful to normalize the price of the consumption good to 1 at each node and we denote by q(s t ) R J the asset prices at node s t. t=0 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
4 Economic application (cont) A financial markets equilibrium consists of prices (q(s t )) T 1 t=0 and agents choices (c h (s t ), θ h (s t )) h=1,...,h such that markets clear, i.e. for all agents h, (θ h, c h ) arg max U h (c) s.t. c(s t ) = e h (s t ) + θ(s t 1 )(q(s t ) + d(s t )) θ(s t )q(s t ) θ(s T ) = 0 for all s T θ(s 1 ) = 0 and for all s t, t < T H θ h (s t ) = 0. h=1 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
5 Economic application (cont) Can write down system of Euler equations and market clearing. If d j (.) are close to collinear, this will be very ill-conditioned For the case of complete markets better to solve with Negishi s method Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
6 Newton s method Suppose that f : R n R n is continuously differentiable. Let z satisfy f (z ) = 0. Suppose D z f (z) is non-singular, define N f (z) = z (D z f (z)) 1 f (z) Given some z 0 define a sequence (z i ) by z i+1 = N f (z i ), i = 0,..., assuming that D z f is non-singular on the entire sequence. If z 0 sufficiently close to z then z i converges to z. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
7 Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
8 Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
9 Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
10 Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
11 Newton s method We say that a point x is in the convergence radius of Newton s method (sometimes people say x is an approximate zero) if the sequence x 0 = x and x i+1 = N f (x i ) is defined for all i = 0, 1, 2,..., and if there is a z such that f (z) = 0 and x i z 1 z x. 2 2i 1 Two obvious questions: Can we determine if x 0 is an approximate zero? What if we do have a good starting point? Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
12 Smale s alpha Let D R n be open and let f : D R n be analytic. For z D, define f (k) (z) to be the k th derivative of f at z. This is a multi-linear operator which maps k-tuples of vectors in D into R n. Define the norm of an operator A to be Ax A = sup x 0 x. Suppose that the Jacobian of f at z, f (1) (z) is invertible and define γ(z) = sup k 2 (f (1) (z)) 1 f (k) (z) k! 1 (k 1) and β(z) = (f (1) (z)) 1 f (z). Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
13 Smale s alpha theorem Theorem Given a z D, suppose the ball of radius (1 contained in D and that Then there exists a z D with β( z)γ( z) < f ( z) = 0 and z z 2β( z). 2 2 )/γ( z) around z is Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
14 Better convergence for NM - univariate case Note that for the one-variable case if we know that f (a) 0 and f (b) 0 for some a < b it is trivial to find a zero in [a, b] via bisection: If f ( a+b a+b a+b 2 ) 0 let a = 2, otherwise let b = 2 and repeat. T his can be combined with Newton s method by discarding a Newton-iterate whenever it lies outside of the interval in which it is known a root lies. Eventually, Newton s method will make the bisection step unnecessary and we get the quadratic convergence (which is much faster than the linear convergence of bisection). Unfortunately this does not generalize to several dimensions Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
15 Better convergence for NM - univariate case (cont.) One simple idea that generalizes to several dimensions is to fix some small δ > 0 and to replace the Newton iteration by requiring x i+1 = x i f (x i) δβ, where β = sgn(f (x i )) if f (x i ) < δ and β = f (x i ) otherwise. This alone will imply that, depending on δ NM does not explode, but it will not ensure convergence. One needs to ensure that in each iterate we get closer to a zero. One way to do this is to ensure that f (x) 2 becomes smaller: x i+1 = x i α if (x i ) δβ. where α i is chosen to ensure that f (x i+1 ) 2 < f (x i ) 2. It is true that it is not obvious how to find an α i like this but there are efficient methods to do this and this idea generalizes to several dimensions. Does not always work! Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
16 Bad Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
17 Bad Newton Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
18 Better convergence for NM Obviously one can view the quest of finding an x such that f (x ) = 0 as 1 min f (x) = x 2 f (x)t f (x) Denote the gradient of f by g i.e. g(x) = D x f (x) = (Dx f (x)) T f (x). We write NM somewhat differently: x i+1 = x i + α i p i where α i is a scalar that gives us the step-length and p i gives the direction. Above we obviously have D x f (x i )p i = f (x i ) Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
19 Better convergence for NM (cont.) As in the one-dimensional case, we want to ensure that the Newton-step decreases f, i.e. we impose for some ɛ > 0. g(x i ) T p i g(x i ) p i ɛ We also want to ensure that the step-length α i is neither too large (and takes us away from the solution) or too small. One way to do this is to impose g(x i + αp i ) T p i ηg(x i ) T p i It can be shown that (under some additional mild conditions) this method gives a sequence of x i such that g(x i ) 0. If D f (x i ) is invertible this implies that f (x) = 0 and we are done. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
20 Better convergence for NM (concl.) It is strong assumption to impose invertibility of D x f everywhere (it is not enough to have it at x, obviously, since we might not reach x ). The idea out is as follows: ione can obtain the Newton step, p i by solving (D x f (x i )) T D x f (x i )p i = (D x f (x i )) T f (x i ) if the Jacobian is non-singular. If it is singular, one can solve instead ( ) (D x f (x i )) T D x f (x i ) + λ i I p i = (D x f (x i )) T f (x i ). For λ i > 0 this always has a unique solution and if on picks the λ i cleverly this can lead to x. Homotopy methods... Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
21 NM - Practical issues Always important to have a good starting point. It pays to first solve simple problems and use solution as starting point to more complicated ones Evaluation of the Jacobian can be very costly. Even if analytic derivatives are available Alternative is to use quasi-newton methods (e.g. Broyden) that do not need the Jacobian at every step Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
22 Non-linear equations - Solvers Important to have a good method to solve non-linear equations! fsolve in Matlab is getting better, used to be horrible (check matlab version) KNITRO, NAG, IPOPT are alternatives which should be taken seriously. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
23 Very quick outline of homotopy methods 1 Let X, Y R k. Two mappings f, g : X Y are called homotopic if there exists a smooth map H : X [0, 1] Y with H(x, 0) = f (x) and H(x, 1) = g(x) for all x X. The map H is called a (smooth) homotopy. Sometimes one the solution set is a smooth path that connects a solution to f (x) = 0 to a solution to g(x) = 0 and f (x) = 0 is easy to solve. Can follow that path numerically Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
24 Very quick outline of homotopy methods 2 Given a homotopy function H : R n [0, 1] R n, if D (x,t) H has rank n for all y H 1 (0), then H is called a regular homotopy By the preimage theorem, H 1 (0) only consists of nice paths. Putting it differently, at any t [0, 1) if H(x, t) = 0 and if D x H(x, t) has full rank n we can apply the implicit function theorem and D t x = ( D x H(x, t)) 1 D t H(x, t). If H is regular, D (x,t) H will have rank n and therefore some partial Jacobian (D (x,t) H) i (i.e. taking out one column i of the Jacobian of D (x,t) H) will have full rank and we can imply the implicit function theorem to this. In this case the path might not be strictly increasing in t but that s OK. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
25 Very quick outline of homotopy methods 3 Of course very few of these paths are good paths if we want to follow the path to compute a solution to H(x, 1) = 0. So in addition to making sure that H 1 (0) is a smooth one-dimensional manifolds, we need some more requirements on H(.,.). 1 Unique starting point: There should be a unique solution to H(x, 0) = 0 2 Boundary-free path: For all t [0, 1] the solution set {x : H(x, t) = 0} should be bounded. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
26 Very quick outline of homotopy methods 4 To use this numerically, it is useful to describe the path using an additional parameter, arc-length, which measures the distance moved along the path. Along the solutions to H(x, t) = 0 which originate at H(x, 0) = 0, let y = (x, t) be a function of the arc-length r R +, i.e. y(r) H 1 (0) for all r 0. If ẏ i = dy i (r) dr, since H(y(r)) = 0, by the chain rule n+1 H ẏ i = 0. y i i=1 The solution y(r) also solves the following differential equation, ẏ i = ( 1) i det((d y H(y)) i ) for all i = 1,..., n + 1. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
27 Very quick outline of homotopy methods 5 We use this differential equation to follow the path. Suppose on iteration k we are at y k close to some y with H(y) = 0. For some step-length d k define For some b R n, define ( Q(y) = y k+1 = y k + d k ẏ k H(y) b(y y k ) Apply Newton s method to this function, taking b = ẏ k. ) Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
28 Very quick outline of Gröbner bases Although not the main focus of this class, sometimes algbraic methods can be useful Can compute roots with arbitrary precision Can find all solutions See Kubler and Schmedders (2010, OR) or Renner, Kubler and Schmedders in Handbook of Computational Economics III Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
29 Polynomials Monomial in x 1, x 2,..., x n : x α x α 1 1 x α x n αn. Exponents α = (α 1, α 2,..., α n ) Z N + Polynomial f in the n variables x 1, x 2,..., x n is a linear combination of finitely many monomials with coefficients in a field K f (x) = α S a α x α, a α K, S Z N + finite Examples of K: Q, R, C Write f K[x 1,..., x n ] Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
30 Polynomial Equation Solving Objective: find all (positive) real solutions to f (x) = 0 Study of polynomial equations on algebraically closed fields Field R is not algebraically closed, so interpret f : C n C n Define solution set V (f 1, f 2,..., f n ) = {x C n : f 1 (x) = f 2 (x) =... = f n (x) = 0} Polynomial ideal is f 1,..., f n is one basis of I I = f 1,..., f n = { n h i f i : h i K[x]} i=1 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
31 Polynomial Equation Solving (cont.) Obviously a given ideal can have different bases, i.e. for polynomials g 1,..., g k and f 1,..., f n g 1,..., g k = f 1,..., f n One basis with nice properties is the so called lexicographic Gröbner basis Why do we care? Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
32 Polynomial Equation Solving (cont.) Obviously a given ideal can have different bases, i.e. for polynomials g 1,..., g k and f 1,..., f n g 1,..., g k = f 1,..., f n One basis with nice properties is the so called lexicographic Gröbner basis Why do we care? If g 1,..., g k = f 1,..., f n then V (f 1,..., f n ) = V (g 1,..., g k ) To solve a system of equations, find another basis which has nice properties, e.g. is triangular Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
33 Shape Lemma and Gröbner basis Let I = f 1, f 2,..., f n be a radical zero dimensional polynomial ideal. Let G denote the (lexicographic) Gröbner basis of I. Suppose all roots have distinct value for last coordinate x n THEN G = {x 1 v 1 (x n ), x 2 v 2 (x n ),..., x n 1 v n 1 (x n ), r(x n )} Polynomial r has degree d, polynomials v i have degrees less than d Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
34 Buchberger s Algorithm Buchberger s algorithm allows calculation of Gröbner bases If all coefficients of f 1,..., f n are rational then the polynomials r, v 1, v 2,..., v n 1 have rational coefficients and can be computed exactly! Solving f 1 (x) = f 2 (x) =... = f n (x) = 0 reduces to solving r(x n ) = 0 Software SINGULAR computes Gröbner basis and numerically approximates all solutions Available free of charge at Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
35 Shape lemma in SINGULAR Consider the following simple example: x yz 3 2z = x + yz 3z + 4 = x + yz 9 = 0 ring R = 0, (x, y, z), lp; ideal I = ( x y z 3 2 z 3 + 1, x + y z 3 z + 4, x + y z 9); groebner(i); Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
36 Shape lemma in SINGULAR Consider the following simple example: x yz 3 2z = x + yz 3z + 4 = x + yz 9 = 0 ring R = 0, (x, y, z), lp; ideal I = ( x y z 3 2 z 3 + 1, x + y z 3 z + 4, x + y z 9); groebner(i); [1] = 2z11 + 3z9 5z8 + 5z3 4z2 1 [2] = 2y +18z10+25z8 45z7 5z6+5z5 5z4+5z3+40z2 31z 6 [3] = 2x 2z9 5z7 + 5z6 5z5 + 5z4 5z3 + 5z2 + 1 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
37 Parameter Shape Lemma - Assumptions What if last equation reads ex + yz 9 = 0 with e being a parameter? Let E R m, be an open set of parameters, (x 1,..., x n ) C n a set of variables and let f 1,..., f n K[e 1,..., e m ; x 1,..., x n ], K R. Assume that for each ē = (ē 1,..., ē m ) E, the ideal I(ē) = f 1 (ē; ),..., f n (ē; ) is zero-dimensional and radical. Furthermore, assume that there exist u 1,..., u n K, such that for all ē any solutions x x satisfying f 1 (ē; x) =... = f n (ē; x) = 0 = f 1 (ē; x ) =... = f n (ē; x ) also satisfy i u i x i i u i x i. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
38 Parameter Shape Lemma - Result There exist r, v 1,..., v n K[e; y] and ρ 1,..., ρ n K[e] such that for y = i u ix i and for all ē outside a closed lower-dimensional subset E 0 of E, {x C n : f 1 (ē, x) =... = f n (ē, x) = 0} {x C n : ρ 1 (ē)x 1 = v 1 (ē; y),..., ρ n (ē)x n = v n (ē; y) for r(ē; y) = 0}. Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
39 Shape lemma with parameters in SINGULAR ring R= (0, e), (x, y, z), lp; ideal I = ( x y z 3 2 z 3 + 1, x + y z 3 z + 4, e x + y z 9); groebner(i); Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
40 Shape lemma with parameters in SINGULAR ring R= (0, e), (x, y, z), lp; ideal I = ( x y z 3 2 z 3 + 1, x + y z 3 z + 4, e x + y z 9); groebner(i); [1] = 2 z z9 5 z8 + (5e) z3 + ( 4e) z2 + ( e) [2] = ( e2 e) y + ( 8e 10) z10 + ( 10e 15) z8 + (20e + 25) z7 + (5e) z6 + ( 5e) z5 + (5e) z4 + ( 5e) z3 + ( 20e2 20e) z2 + (16e2 + 15e) z + (3e2 + 3e) [3] = ( e 1) x +2 z9+5 z7 5 z6+5 z5 5 z4+5 z3 5 z2 1 Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
41 An example in matlab (and Singular) Matlab-command fsolve can be used to solve non-linear equations numerically Might need a pretty good guess :) Example: x 2 + 2y 2 5x + 7y = 40, 3x 2 y 2 + 4x + 2y = 28 Write as function in matlab... Call with guess = [2, 3] [result, fval, exitflag, output] = fsolve(@eqns, guess) Felix Kubler Comp.Econ. Gerzensee, Ch2 October 7, / 38
Competitive Equilibria in Semi-Algebraic Economies
Competitive Equilibria in Semi-Algebraic Economies Felix Kubler Swiss Banking Institute University of Zurich and Swiss Finance Institute kubler@isb.uzh.ch Karl Schmedders Institute for Operations Research
More informationIntroduction, basic but important concepts
Introduction, basic but important concepts Felix Kubler 1 1 DBF, University of Zurich and Swiss Finance Institute October 7, 2017 Felix Kubler Comp.Econ. Gerzensee, Ch1 October 7, 2017 1 / 31 Economics
More informationCompetitive Equilibria in Semi-Algebraic Economies
Competitive Equilibria in Semi-Algebraic Economies Felix Kubler Department of Economics University of Pennsylvania kubler@sas.upenn.edu Karl Schmedders Kellogg MEDS Northwestern University k-schmedders@kellogg.northwestern.edu
More informationProjection Methods. Felix Kubler 1. October 10, DBF, University of Zurich and Swiss Finance Institute
Projection Methods Felix Kubler 1 1 DBF, University of Zurich and Swiss Finance Institute October 10, 2017 Felix Kubler Comp.Econ. Gerzensee, Ch5 October 10, 2017 1 / 55 Motivation In many dynamic economic
More informationNumerical Methods I Solving Nonlinear Equations
Numerical Methods I Solving Nonlinear Equations Aleksandar Donev Courant Institute, NYU 1 donev@courant.nyu.edu 1 MATH-GA 2011.003 / CSCI-GA 2945.003, Fall 2014 October 16th, 2014 A. Donev (Courant Institute)
More informationApplied Computational Economics Workshop. Part 3: Nonlinear Equations
Applied Computational Economics Workshop Part 3: Nonlinear Equations 1 Overview Introduction Function iteration Newton s method Quasi-Newton methods Practical example Practical issues 2 Introduction Nonlinear
More informationNegishi s method for stochastic OLG models
Johannes Brumm University of Zurich Felix Kubler University of Zurich QSPS, May 2013 Motivation OLG models are important tools in macro and public finance Unfortunately, humans typically live for 80 years...
More informationHigh-dimensional Problems in Finance and Economics. Thomas M. Mertens
High-dimensional Problems in Finance and Economics Thomas M. Mertens NYU Stern Risk Economics Lab April 17, 2012 1 / 78 Motivation Many problems in finance and economics are high dimensional. Dynamic Optimization:
More informationCS 542G: Robustifying Newton, Constraints, Nonlinear Least Squares
CS 542G: Robustifying Newton, Constraints, Nonlinear Least Squares Robert Bridson October 29, 2008 1 Hessian Problems in Newton Last time we fixed one of plain Newton s problems by introducing line search
More informationPROJECTION METHODS FOR DYNAMIC MODELS
PROJECTION METHODS FOR DYNAMIC MODELS Kenneth L. Judd Hoover Institution and NBER June 28, 2006 Functional Problems Many problems involve solving for some unknown function Dynamic programming Consumption
More informationLinear Algebra Massoud Malek
CSUEB Linear Algebra Massoud Malek Inner Product and Normed Space In all that follows, the n n identity matrix is denoted by I n, the n n zero matrix by Z n, and the zero vector by θ n An inner product
More informationUnconstrained optimization
Chapter 4 Unconstrained optimization An unconstrained optimization problem takes the form min x Rnf(x) (4.1) for a target functional (also called objective function) f : R n R. In this chapter and throughout
More informationLMI Methods in Optimal and Robust Control
LMI Methods in Optimal and Robust Control Matthew M. Peet Arizona State University Lecture 15: Nonlinear Systems and Lyapunov Functions Overview Our next goal is to extend LMI s and optimization to nonlinear
More informationNumerical Algorithms as Dynamical Systems
A Study on Numerical Algorithms as Dynamical Systems Moody Chu North Carolina State University What This Study Is About? To recast many numerical algorithms as special dynamical systems, whence to derive
More informationFirst-Order Ordinary Differntial Equations II: Autonomous Case. David Levermore Department of Mathematics University of Maryland.
First-Order Ordinary Differntial Equations II: Autonomous Case David Levermore Department of Mathematics University of Maryland 25 February 2009 These notes cover some of the material that we covered in
More informationPenalty and Barrier Methods. So we again build on our unconstrained algorithms, but in a different way.
AMSC 607 / CMSC 878o Advanced Numerical Optimization Fall 2008 UNIT 3: Constrained Optimization PART 3: Penalty and Barrier Methods Dianne P. O Leary c 2008 Reference: N&S Chapter 16 Penalty and Barrier
More informationminimize x subject to (x 2)(x 4) u,
Math 6366/6367: Optimization and Variational Methods Sample Preliminary Exam Questions 1. Suppose that f : [, L] R is a C 2 -function with f () on (, L) and that you have explicit formulae for
More informationRecursive equilibria in dynamic economies with stochastic production
Recursive equilibria in dynamic economies with stochastic production Johannes Brumm DBF, University of Zurich johannes.brumm@googlemail.com Dominika Kryczka DBF, University of Zurich and Swiss Finance
More informationSMSTC (2017/18) Geometry and Topology 2.
SMSTC (2017/18) Geometry and Topology 2 Lecture 1: Differentiable Functions and Manifolds in R n Lecturer: Diletta Martinelli (Notes by Bernd Schroers) a wwwsmstcacuk 11 General remarks In this lecture
More informationMath 215B: Solutions 3
Math 215B: Solutions 3 (1) For this problem you may assume the classification of smooth one-dimensional manifolds: Any compact smooth one-dimensional manifold is diffeomorphic to a finite disjoint union
More informationKey Concepts: Economic Computation, Part III
Key Concepts: Economic Computation, Part III Brent Hickman Summer, 8 1 Using Newton s Method to Find Roots of Real- Valued Functions The intuition behind Newton s method is that finding zeros of non-linear
More informationIE 5531: Engineering Optimization I
IE 5531: Engineering Optimization I Lecture 19: Midterm 2 Review Prof. John Gunnar Carlsson November 22, 2010 Prof. John Gunnar Carlsson IE 5531: Engineering Optimization I November 22, 2010 1 / 34 Administrivia
More informationSearch Directions for Unconstrained Optimization
8 CHAPTER 8 Search Directions for Unconstrained Optimization In this chapter we study the choice of search directions used in our basic updating scheme x +1 = x + t d. for solving P min f(x). x R n All
More informationMathematical Analysis Outline. William G. Faris
Mathematical Analysis Outline William G. Faris January 8, 2007 2 Chapter 1 Metric spaces and continuous maps 1.1 Metric spaces A metric space is a set X together with a real distance function (x, x ) d(x,
More informationCHAPTER 10: Numerical Methods for DAEs
CHAPTER 10: Numerical Methods for DAEs Numerical approaches for the solution of DAEs divide roughly into two classes: 1. direct discretization 2. reformulation (index reduction) plus discretization Direct
More informationAlberto Bressan. Department of Mathematics, Penn State University
Non-cooperative Differential Games A Homotopy Approach Alberto Bressan Department of Mathematics, Penn State University 1 Differential Games d dt x(t) = G(x(t), u 1(t), u 2 (t)), x(0) = y, u i (t) U i
More informationMath 203A - Solution Set 1
Math 203A - Solution Set 1 Problem 1. Show that the Zariski topology on A 2 is not the product of the Zariski topologies on A 1 A 1. Answer: Clearly, the diagonal Z = {(x, y) : x y = 0} A 2 is closed in
More informationMathematical Economics: Lecture 2
Mathematical Economics: Lecture 2 Yu Ren WISE, Xiamen University September 25, 2012 Outline 1 Number Line The number line, origin (Figure 2.1 Page 11) Number Line Interval (a, b) = {x R 1 : a < x < b}
More informationNon-parametric counterfactual analysis in dynamic general equilibrium
Non-parametric counterfactual analysis in dynamic general equilibrium Felix Kubler Department of Economics University of Pennsylvania fkubler@gmail.com Karl Schmedders Kellogg MEDS Northwestern University
More informationB553 Lecture 3: Multivariate Calculus and Linear Algebra Review
B553 Lecture 3: Multivariate Calculus and Linear Algebra Review Kris Hauser December 30, 2011 We now move from the univariate setting to the multivariate setting, where we will spend the rest of the class.
More informationNonlinear Programming
Nonlinear Programming Kees Roos e-mail: C.Roos@ewi.tudelft.nl URL: http://www.isa.ewi.tudelft.nl/ roos LNMB Course De Uithof, Utrecht February 6 - May 8, A.D. 2006 Optimization Group 1 Outline for week
More informationADVANCED TOPICS IN ALGEBRAIC GEOMETRY
ADVANCED TOPICS IN ALGEBRAIC GEOMETRY DAVID WHITE Outline of talk: My goal is to introduce a few more advanced topics in algebraic geometry but not to go into too much detail. This will be a survey of
More informationImplicit Functions, Curves and Surfaces
Chapter 11 Implicit Functions, Curves and Surfaces 11.1 Implicit Function Theorem Motivation. In many problems, objects or quantities of interest can only be described indirectly or implicitly. It is then
More information1. Nonlinear Equations. This lecture note excerpted parts from Michael Heath and Max Gunzburger. f(x) = 0
Numerical Analysis 1 1. Nonlinear Equations This lecture note excerpted parts from Michael Heath and Max Gunzburger. Given function f, we seek value x for which where f : D R n R n is nonlinear. f(x) =
More informationScientific Computing: An Introductory Survey
Scientific Computing: An Introductory Survey Chapter 5 Nonlinear Equations Prof. Michael T. Heath Department of Computer Science University of Illinois at Urbana-Champaign Copyright c 2002. Reproduction
More informationPolynomials, Ideals, and Gröbner Bases
Polynomials, Ideals, and Gröbner Bases Notes by Bernd Sturmfels for the lecture on April 10, 2018, in the IMPRS Ringvorlesung Introduction to Nonlinear Algebra We fix a field K. Some examples of fields
More informationEcon Slides from Lecture 10
Econ 205 Sobel Econ 205 - Slides from Lecture 10 Joel Sobel September 2, 2010 Example Find the tangent plane to {x x 1 x 2 x 2 3 = 6} R3 at x = (2, 5, 2). If you let f (x) = x 1 x 2 x3 2, then this is
More informationTwo hours. To be provided by Examinations Office: Mathematical Formula Tables. THE UNIVERSITY OF MANCHESTER. 29 May :45 11:45
Two hours MATH20602 To be provided by Examinations Office: Mathematical Formula Tables. THE UNIVERSITY OF MANCHESTER NUMERICAL ANALYSIS 1 29 May 2015 9:45 11:45 Answer THREE of the FOUR questions. If more
More information1 Bewley Economies with Aggregate Uncertainty
1 Bewley Economies with Aggregate Uncertainty Sofarwehaveassumedawayaggregatefluctuations (i.e., business cycles) in our description of the incomplete-markets economies with uninsurable idiosyncratic risk
More informationLECTURE NOTES ELEMENTARY NUMERICAL METHODS. Eusebius Doedel
LECTURE NOTES on ELEMENTARY NUMERICAL METHODS Eusebius Doedel TABLE OF CONTENTS Vector and Matrix Norms 1 Banach Lemma 20 The Numerical Solution of Linear Systems 25 Gauss Elimination 25 Operation Count
More informationScientific Computing: Optimization
Scientific Computing: Optimization Aleksandar Donev Courant Institute, NYU 1 donev@courant.nyu.edu 1 Course MATH-GA.2043 or CSCI-GA.2112, Spring 2012 March 8th, 2011 A. Donev (Courant Institute) Lecture
More informationTrust Regions. Charles J. Geyer. March 27, 2013
Trust Regions Charles J. Geyer March 27, 2013 1 Trust Region Theory We follow Nocedal and Wright (1999, Chapter 4), using their notation. Fletcher (1987, Section 5.1) discusses the same algorithm, but
More informationTopic # /31 Feedback Control Systems. Analysis of Nonlinear Systems Lyapunov Stability Analysis
Topic # 16.30/31 Feedback Control Systems Analysis of Nonlinear Systems Lyapunov Stability Analysis Fall 010 16.30/31 Lyapunov Stability Analysis Very general method to prove (or disprove) stability of
More informationMath 203A - Solution Set 1
Math 203A - Solution Set 1 Problem 1. Show that the Zariski topology on A 2 is not the product of the Zariski topologies on A 1 A 1. Answer: Clearly, the diagonal Z = {(x, y) : x y = 0} A 2 is closed in
More informationBasic facts and definitions
Synopsis Thursday, September 27 Basic facts and definitions We have one one hand ideals I in the polynomial ring k[x 1,... x n ] and subsets V of k n. There is a natural correspondence. I V (I) = {(k 1,
More informationFIXED POINT ITERATIONS
FIXED POINT ITERATIONS MARKUS GRASMAIR 1. Fixed Point Iteration for Non-linear Equations Our goal is the solution of an equation (1) F (x) = 0, where F : R n R n is a continuous vector valued mapping in
More informationECON 5111 Mathematical Economics
Test 1 October 1, 2010 1. Construct a truth table for the following statement: [p (p q)] q. 2. A prime number is a natural number that is divisible by 1 and itself only. Let P be the set of all prime numbers
More informationMATH 51H Section 4. October 16, Recall what it means for a function between metric spaces to be continuous:
MATH 51H Section 4 October 16, 2015 1 Continuity Recall what it means for a function between metric spaces to be continuous: Definition. Let (X, d X ), (Y, d Y ) be metric spaces. A function f : X Y is
More informationDiscussion Papers in Economics
Discussion Papers in Economics No. 10/11 A General Equilibrium Corporate Finance Theorem for Incomplete Markets: A Special Case By Pascal Stiefenhofer, University of York Department of Economics and Related
More informationECS550NFB Introduction to Numerical Methods using Matlab Day 2
ECS550NFB Introduction to Numerical Methods using Matlab Day 2 Lukas Laffers lukas.laffers@umb.sk Department of Mathematics, University of Matej Bel June 9, 2015 Today Root-finding: find x that solves
More informationCS 450 Numerical Analysis. Chapter 5: Nonlinear Equations
Lecture slides based on the textbook Scientific Computing: An Introductory Survey by Michael T. Heath, copyright c 2018 by the Society for Industrial and Applied Mathematics. http://www.siam.org/books/cl80
More informationTHE INVERSE FUNCTION THEOREM
THE INVERSE FUNCTION THEOREM W. PATRICK HOOPER The implicit function theorem is the following result: Theorem 1. Let f be a C 1 function from a neighborhood of a point a R n into R n. Suppose A = Df(a)
More informationRegularity of competitive equilibria in a production economy with externalities
Regularity of competitive equilibria in a production economy with externalities Elena del Mercato Vincenzo Platino Paris School of Economics - Université Paris 1 Panthéon Sorbonne QED-Jamboree Copenhagen,
More information10. Smooth Varieties. 82 Andreas Gathmann
82 Andreas Gathmann 10. Smooth Varieties Let a be a point on a variety X. In the last chapter we have introduced the tangent cone C a X as a way to study X locally around a (see Construction 9.20). It
More information10.34 Numerical Methods Applied to Chemical Engineering Fall Quiz #1 Review
10.34 Numerical Methods Applied to Chemical Engineering Fall 2015 Quiz #1 Review Study guide based on notes developed by J.A. Paulson, modified by K. Severson Linear Algebra We ve covered three major topics
More informationCSL361 Problem set 4: Basic linear algebra
CSL361 Problem set 4: Basic linear algebra February 21, 2017 [Note:] If the numerical matrix computations turn out to be tedious, you may use the function rref in Matlab. 1 Row-reduced echelon matrices
More informationLecture 3: Huggett s 1993 model. 1 Solving the savings problem for an individual consumer
UNIVERSITY OF WESTERN ONTARIO LONDON ONTARIO Paul Klein Office: SSC 4044 Extension: 85484 Email: pklein2@uwo.ca URL: http://paulklein.ca/newsite/teaching/619.php Economics 9619 Computational methods in
More informationELLIPTIC CURVES SEMINAR: SIEGEL S THEOREM
ELLIPTIC CURVES SEMINAR: SIEGEL S THEOREM EVAN WARNER 1. Siegel s Theorem over Q 1.1. Statement of theorems. Siegel s theorem, in its simplest form, is the fact that a nonsingular elliptic curve contains
More informationOutline. Scientific Computing: An Introductory Survey. Nonlinear Equations. Nonlinear Equations. Examples: Nonlinear Equations
Methods for Systems of Methods for Systems of Outline Scientific Computing: An Introductory Survey Chapter 5 1 Prof. Michael T. Heath Department of Computer Science University of Illinois at Urbana-Champaign
More informationAlgebraic Geometry for CAGD
Chapter 17 Algebraic Geometry for CAGD Initially, the field of computer aided geometric design and graphics drew most heavily from differential geometry, approximation theory, and vector geometry. Since
More informationPartial Fractions. June 27, In this section, we will learn to integrate another class of functions: the rational functions.
Partial Fractions June 7, 04 In this section, we will learn to integrate another class of functions: the rational functions. Definition. A rational function is a fraction of two polynomials. For example,
More informationB ɛ (P ) B. n N } R. Q P
8. Limits Definition 8.1. Let P R n be a point. The open ball of radius ɛ > 0 about P is the set B ɛ (P ) = { Q R n P Q < ɛ }. The closed ball of radius ɛ > 0 about P is the set { Q R n P Q ɛ }. Definition
More informationHigher-Order Dynamics in Asset-Pricing Models with Recursive Preferences
Higher-Order Dynamics in Asset-Pricing Models with Recursive Preferences Walt Pohl Karl Schmedders Ole Wilms Dept. of Business Administration, University of Zurich Becker Friedman Institute Computational
More informationPREMUR Seminar Week 2 Discussions - Polynomial Division, Gröbner Bases, First Applications
PREMUR 2007 - Seminar Week 2 Discussions - Polynomial Division, Gröbner Bases, First Applications Day 1: Monomial Orders In class today, we introduced the definition of a monomial order in the polyomial
More information2.4. Solving ideal problems by Gröbner bases
Computer Algebra, F.Winkler, WS 2010/11 2.4. Solving ideal problems by Gröbner bases Computation in the vector space of polynomials modulo an ideal The ring K[X] /I of polynomials modulo the ideal I is
More informationPrinciples of Optimal Control Spring 2008
MIT OpenCourseWare http://ocw.mit.edu 16.323 Principles of Optimal Control Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms. 16.323 Lecture
More informationDynamic Programming with Hermite Interpolation
Dynamic Programming with Hermite Interpolation Yongyang Cai Hoover Institution, 424 Galvez Mall, Stanford University, Stanford, CA, 94305 Kenneth L. Judd Hoover Institution, 424 Galvez Mall, Stanford University,
More informationQUALIFYING EXAMINATION Harvard University Department of Mathematics Tuesday September 21, 2004 (Day 1)
QUALIFYING EXAMINATION Harvard University Department of Mathematics Tuesday September 21, 2004 (Day 1) Each of the six questions is worth 10 points. 1) Let H be a (real or complex) Hilbert space. We say
More informationTEST CODE: PMB SYLLABUS
TEST CODE: PMB SYLLABUS Convergence and divergence of sequence and series; Cauchy sequence and completeness; Bolzano-Weierstrass theorem; continuity, uniform continuity, differentiability; directional
More information8. Prime Factorization and Primary Decompositions
70 Andreas Gathmann 8. Prime Factorization and Primary Decompositions 13 When it comes to actual computations, Euclidean domains (or more generally principal ideal domains) are probably the nicest rings
More informationMulti-Robotic Systems
CHAPTER 9 Multi-Robotic Systems The topic of multi-robotic systems is quite popular now. It is believed that such systems can have the following benefits: Improved performance ( winning by numbers ) Distributed
More informationSeptember Math Course: First Order Derivative
September Math Course: First Order Derivative Arina Nikandrova Functions Function y = f (x), where x is either be a scalar or a vector of several variables (x,..., x n ), can be thought of as a rule which
More informationTangent spaces, normals and extrema
Chapter 3 Tangent spaces, normals and extrema If S is a surface in 3-space, with a point a S where S looks smooth, i.e., without any fold or cusp or self-crossing, we can intuitively define the tangent
More informationIntroduction to Gröbner Bases for Geometric Modeling. Geometric & Solid Modeling 1989 Christoph M. Hoffmann
Introduction to Gröbner Bases for Geometric Modeling Geometric & Solid Modeling 1989 Christoph M. Hoffmann Algebraic Geometry Branch of mathematics. Express geometric facts in algebraic terms in order
More information15. Polynomial rings Definition-Lemma Let R be a ring and let x be an indeterminate.
15. Polynomial rings Definition-Lemma 15.1. Let R be a ring and let x be an indeterminate. The polynomial ring R[x] is defined to be the set of all formal sums a n x n + a n 1 x n +... a 1 x + a 0 = a
More informationEuler Equations: local existence
Euler Equations: local existence Mat 529, Lesson 2. 1 Active scalars formulation We start with a lemma. Lemma 1. Assume that w is a magnetization variable, i.e. t w + u w + ( u) w = 0. If u = Pw then u
More informationImmerse Metric Space Homework
Immerse Metric Space Homework (Exercises -2). In R n, define d(x, y) = x y +... + x n y n. Show that d is a metric that induces the usual topology. Sketch the basis elements when n = 2. Solution: Steps
More informationPolynomial mappings into a Stiefel manifold and immersions
Polynomial mappings into a Stiefel manifold and immersions Iwona Krzyżanowska Zbigniew Szafraniec November 2011 Abstract For a polynomial mapping from S n k to the Stiefel manifold Ṽk(R n ), where n k
More informationOn the minimal free resolution of a monomial ideal.
On the minimal free resolution of a monomial ideal. Caitlin M c Auley August 2012 Abstract Given a monomial ideal I in the polynomial ring S = k[x 1,..., x n ] over a field k, we construct a minimal free
More informationOptimization and Calculus
Optimization and Calculus To begin, there is a close relationship between finding the roots to a function and optimizing a function. In the former case, we solve for x. In the latter, we solve: g(x) =
More informationChapter 4. Inverse Function Theorem. 4.1 The Inverse Function Theorem
Chapter 4 Inverse Function Theorem d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d dd d d d d This chapter
More informationEAD 115. Numerical Solution of Engineering and Scientific Problems. David M. Rocke Department of Applied Science
EAD 115 Numerical Solution of Engineering and Scientific Problems David M. Rocke Department of Applied Science Taylor s Theorem Can often approximate a function by a polynomial The error in the approximation
More information1. Using the model and notations covered in class, the expected returns are:
Econ 510a second half Yale University Fall 2006 Prof. Tony Smith HOMEWORK #5 This homework assignment is due at 5PM on Friday, December 8 in Marnix Amand s mailbox. Solution 1. a In the Mehra-Prescott
More informationCertified predictor-corrector tracking for Newton homotopies
Certified predictor-corrector tracking for Newton homotopies Jonathan D. Hauenstein Alan C. Liddell, Jr. March 11, 2014 Abstract We develop certified tracking procedures for Newton homotopies, which are
More informationLecture Notes to Accompany. Scientific Computing An Introductory Survey. by Michael T. Heath. Chapter 5. Nonlinear Equations
Lecture Notes to Accompany Scientific Computing An Introductory Survey Second Edition by Michael T Heath Chapter 5 Nonlinear Equations Copyright c 2001 Reproduction permitted only for noncommercial, educational
More informationNonlinear equations. Norms for R n. Convergence orders for iterative methods
Nonlinear equations Norms for R n Assume that X is a vector space. A norm is a mapping X R with x such that for all x, y X, α R x = = x = αx = α x x + y x + y We define the following norms on the vector
More informationNumerical solutions of nonlinear systems of equations
Numerical solutions of nonlinear systems of equations Tsung-Ming Huang Department of Mathematics National Taiwan Normal University, Taiwan E-mail: min@math.ntnu.edu.tw August 28, 2011 Outline 1 Fixed points
More informationDiscrete State Space Methods for Dynamic Economies
Discrete State Space Methods for Dynamic Economies A Brief Introduction Craig Burnside Duke University September 2006 Craig Burnside (Duke University) Discrete State Space Methods September 2006 1 / 42
More informationComplex Systems Workshop Lecture III: Behavioral Asset Pricing Model with Heterogeneous Beliefs
Complex Systems Workshop Lecture III: Behavioral Asset Pricing Model with Heterogeneous Beliefs Cars Hommes CeNDEF, UvA CEF 2013, July 9, Vancouver Cars Hommes (CeNDEF, UvA) Complex Systems CEF 2013, Vancouver
More informationALGEBRAIC GEOMETRY COURSE NOTES, LECTURE 2: HILBERT S NULLSTELLENSATZ.
ALGEBRAIC GEOMETRY COURSE NOTES, LECTURE 2: HILBERT S NULLSTELLENSATZ. ANDREW SALCH 1. Hilbert s Nullstellensatz. The last lecture left off with the claim that, if J k[x 1,..., x n ] is an ideal, then
More informationCS 257: Numerical Methods
CS 57: Numerical Methods Final Exam Study Guide Version 1.00 Created by Charles Feng http://www.fenguin.net CS 57: Numerical Methods Final Exam Study Guide 1 Contents 1 Introductory Matter 3 1.1 Calculus
More informationIterative Methods. Splitting Methods
Iterative Methods Splitting Methods 1 Direct Methods Solving Ax = b using direct methods. Gaussian elimination (using LU decomposition) Variants of LU, including Crout and Doolittle Other decomposition
More informationLecture 4: Completion of a Metric Space
15 Lecture 4: Completion of a Metric Space Closure vs. Completeness. Recall the statement of Lemma??(b): A subspace M of a metric space X is closed if and only if every convergent sequence {x n } X satisfying
More information3 Algebraic Methods. we can differentiate both sides implicitly to obtain a differential equation involving x and y:
3 Algebraic Methods b The first appearance of the equation E Mc 2 in Einstein s handwritten notes. So far, the only general class of differential equations that we know how to solve are directly integrable
More informationHigh Performance Nonlinear Solvers
What is a nonlinear system? High Performance Nonlinear Solvers Michael McCourt Division Argonne National Laboratory IIT Meshfree Seminar September 19, 2011 Every nonlinear system of equations can be described
More informationFinal Examination. CS 205A: Mathematical Methods for Robotics, Vision, and Graphics (Fall 2013), Stanford University
Final Examination CS 205A: Mathematical Methods for Robotics, Vision, and Graphics (Fall 2013), Stanford University The exam runs for 3 hours. The exam contains eight problems. You must complete the first
More information1 The Basic RBC Model
IHS 2016, Macroeconomics III Michael Reiter Ch. 1: Notes on RBC Model 1 1 The Basic RBC Model 1.1 Description of Model Variables y z k L c I w r output level of technology (exogenous) capital at end of
More informationChapter 3. Dynamic Programming
Chapter 3. Dynamic Programming This chapter introduces basic ideas and methods of dynamic programming. 1 It sets out the basic elements of a recursive optimization problem, describes the functional equation
More informationHeterogeneous Agent Models: I
Heterogeneous Agent Models: I Mark Huggett 2 2 Georgetown September, 2017 Introduction Early heterogeneous-agent models integrated the income-fluctuation problem into general equilibrium models. A key
More informationAn introduction to Birkhoff normal form
An introduction to Birkhoff normal form Dario Bambusi Dipartimento di Matematica, Universitá di Milano via Saldini 50, 0133 Milano (Italy) 19.11.14 1 Introduction The aim of this note is to present an
More information