Mathematics and Statistics Preparatory Course for the M.Phil.
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Mathematics and Statistics Preparatory Course for the M.Phil. Economics, M.Phil. Finance and Economics and M.Res. Economics Faculty of Economics, University of Cambridge
May 2022
The four-week Preparatory Course in Mathematics and Statistics is a compulsory component of the M.Phil. programmes in the Faculty of Economics. The aim of the Preparatory Course is to ensure that all students understand the mathematical, sta-tistical and econometric techniques which are used throughout the core and optional modules. We require that all students admitted to the Masters programmes have a firm grasp of basic calculus, linear algebra, and statistics. The Preparatory Course therefore takes such a background as given and both revises and builds upon these topics.
There are four sections to the preparatory course: Linear Algebra, Probability and Statistics, Optimisation and Difference/Differential Equations. Some details of the con-tent of these, including prerequisites and readings, are given below together with some example questions. You should be able to do some of these questions before you arrive and all of them by the end of the course.
Depending on your individual background some of the elements may be more, or less, familiar. So it is vital that you assess your own knowledge and work hard to ensure that you have solid foundations for all this material. Without this you will find the subsequent content of your MPhil course very challenging.
Teaching for the preparatory course is intense. We expect you to refresh your knowledge and skills in mathematics and statistics before you arrive in Cambridge. In particular, you should ensure that you have revised the prerequisite material we include in these notes. You should work on all the exercises below in order to check mastery of this material.
Further examples of problems relating to the material that will be covered in the prepara- tory course can be found on the Faculty’s web site, at
http : //www.econ.cam.ac.uk/graduate/mphil/prep.html
1 Linear Algebra
1.1 Prerequisites
The course is mostly self-contained but some basic knowledge of linear algebra is as- sumed. The primary textbook for this section of the preparatory course is Abadir and Magnus [1]. An alternative discussion of much of this material may be found in Appendix A of Greene [4]. Note that although this is an econometrics textbook such books often contain useful material on linear algebra because of the importance of these methods in econometrics.
A good introductory discussion may be found in Chapter 1 of Binmore and Davies [2] while some more advanced topics, useful for courses throughout the year, are dealt with in the first section of Ostaszewski [7].
1.2 Topics covered in the course
Matrices and vectors, solutions to simultaneous linear equations, square matrices, de- terminants, eigenvalues, eigenvectors diagonalisation positive and negative definite ma- trices.
1.3 Some practice problems
Exercise 1 Find the determinant of the following matrix
l 3 2 6 」
「 .
Exercise 2 Solve the following system of equations using Cramer’s rule:
7x1 − x2 − x3 = 0
10x1 − 2x2 + x3 = 8
6x1 + 3x2 − 2x3 = 7
Exercise 3 Consider the following model of a closed economy with Y gross income, C consumption, I investment, G government expenditure, and a, b parameters .
Y = C + I + G
C = a + bY.
For fixed I and G, solve for equilibrium income and consumption using Cramer’s Rule .
Exercise 4 Find the eigenvalues and eigenvectors of the following 2 × 2 matrix
[ 5 1 ]
2 Probability and Statistics
2.1 Prerequisites
The course assumes students are familiar with the basic concepts of probability and random variables but revises this material from a more mathematical perspective. The material is covered at a very basic level in Ross [9] and in greater detail in Miller and Miller [6]. For more advanced discussion see Chapters 1-9 of Casella and Berger [3] or Chapters 1-6 of Wasserman [11].
2.2 Topics covered in the course
The course covers the basic probability and statistical material that is used in the econometrics course but can also appear in both macroeconomics and microeconomics, or wherever issues of dealing with uncertainty arise.
The main elements that will be covered are:
(i) Probability theory and random variables.
(ii) Distribution functions. Expectations and moments.
(iii) Joint, conditional and marginal distributions.
(iv) Sampling theory and sampling distributions.
(v) Method of moments, least squares and maximum likelihood estimation. (vi) Point estimation, bias and mean squared error. Confidence intervals.
(vii) Statistical inference and hypothesis testing. Type I and Type II errors.
2.3 Some practice problems
Exercise 5 Two fair coins, a 10p and a 50p, are tossed. Find the probabilities of:
1. Both showing heads
2. Different faces showing up
3. At least one head
4. You are told that the 10p shows heads . What is the probability that both show heads?
5. You are told that at least one of the two coins shows heads . What is the probability that both show heads?
6. What is the probability of two sixes when two fair dice are rolled?
7. What is the probability of at least one six when two fair dice are rolled?
Exercise 6 A random variable X has the distribution function
( x2
F (x) = 0
( 1
for
for
for
0 ≤ x ≤ 1
x < 0
x > 1.
Define the probability density of X, and find its mean and standard deviation.
Exercise 7 The following data show the times of flow through an orifice of two types of sand. Is there sufficient evidence that one type flows faster than the other?
Type 1 27.2 26.8 27.4 27.1 26.5
Type 2
29.6
30.0
28.4
30.2
Exercise 8 There are 30 people in a room. What is the probability that two or more have their birthday on the same day of the year?
Exercise 9 The following data are obtained on prices and quantities of oranges sold in a supermarket on 12 consecutive days .
Price:
pence per kilo (X)
100
90
80
70
70
70
70
65
60
60
55
50
Quantity: kilos (Y)
55
70
90
100
90
105
80
110
125
115
130
130
It is postulated that the demand function for oranges is of the form
Yi = α + βXi + ϵi, i = 1, 2, ..., 12 (1)
Write down the least squares objective function and hence obtain the least squares
estimates of α and β i. e . = and = Y − X .
Exercise 10 Random variables X1 and X2 are drawn independently from a distribution with probability density function f(x) and cumulative distribution function F (x) .
(a) Calculate P (X1 ≤ x, X2 ≤ x) in terms of F (x) and hence show that the density
function of max(X1, X2 ) is 2f(x)F (x)
Now suppose that f (x) is the uniform distribution U [0, 1] i. e .
f(x) = 1 0 ≤ x ≤ 1
(b) Calculate F (X) and hence write down the probability density function of the ran-
dom variable Y = max {X1, X2 }.
(c) Show that E (Y ) = and Var (Y ) = .
3 Calculus and Optimisation
3.1 Prerequisites
All students on the M.Phil. programme are expected to have a firm grasp of basic calculus before they arrive in Cambridge. We recommend the following books to review this prerequisite material before you arrive in Cambridge:
• Sydsaeter, K., and P. Hammond, Essential Mathematics for Economic Analysis, Prentice Hall. Chapters 1— 10, 14—20.
• Pemberton, M., and N. Rau, Mathematics for Economists, Manchester University Press. Chapters 1— 14.
See also the lecture notes at http : //www.econ.cam.ac.uk/graduate/mphil/prep.html.
Those who are aiming to continue on to a PhD programme should ideally aim to master this material at a higher level as covered in the Mathematical Appendix (pp. 926–970) of
• Mas-Colell, A., M. Whinston and J. Green, Microeconomic Theory, Oxford Uni- versity Press.
List of prerequisite topics
The specific topics which students will be expected to understand as prerequisites for the Calculus and Optimisation component of the course (which are covered in Sydsaeter and Hammond’s chapters 1— 10, 14—20, and Pemberton and Rau’s chapters 1— 14) are briefly listed below:
1. Basic concepts of logic (including the concept of a proof; necessary and sufficient conditions)
2. Set notation and basic properties of sets
3. Standard secondary school algebra (including manipulation of inequalities, solving quadratic equations, systems of linear equations)
4. Functions and related notation, terminology, and definitions (such as one-to-one, onto, image, inverse image, inverse function, composition of functions, etc.)
5. Functions from R to R, basic properties (such as increasing, decreasing, etc.)
6. Polynomials, basic polynomial algebra, roots, etc.
7. The exponential and the logarithm functions (and other exponents and loga- rithms), basic properties
8. Sequences of real numbers, limits, series
9. Open and closed sets in R, compact sets
10. Single-variable calculus: limits, continuity, concept of derivative, rules of differen- tiation, the chain rule, L’hˆopital’s rule, differentials, integration (including various techniques such as change of variables, integration by parts, etc.), geometric in- terpretation of differentiation and integration, fundamental theorem of calculus, concavity, convexity.
11. Unconstrained and constrained optimisation of functions from R to R, identifica- tion and classification of stationary and extreme values with the use of first order and second order conditions.
12. Taylor series and Taylor approximations for functions from R to R.
13. Rn for n ≥ 2, the notion of distance in Rn, bounded, open, closed, compact sets in Rn
14. Calculus of several variables (i.e., functions from Rn to R), partial differentiation, continuous differentiability and Young’s Theorem; the chain rule and the total derivative; differentials. The envelope theorem.
15. Constrained optimisation of functions of several variables subject to equality con- straints: Lagrange’s method; the interpretation of the Lagrange multiplier.
16. Second-order condition when optimising functions from R2 to R. Convexity/concavity of such functions.
3.2 Topics covered in the course
We will briefly review the above mentioned topics and illustrate these concepts in a range of applied problems. In addition to these topics, we will introduce and illustrate uses of quasi-concavity and quasi-convexity; optimisation with inequality constraints and Kuhn-Tucker conditions; the implicit function theorem; and the envelope theorem for constrained optimisation problems.
3.3 Some Practice Problems
1. Write the following in set notation:
(a) the set of all real numbers greater than 8 and less than 73,
(b) the set of all points on the coordinate plane whose distance from (2 , 5) is
greater than 1 and less than or equal to 2.
2. Given the sets S1 = {2, 4, 6}, S2 = {7, 2, 6}, S3 = {4, 2, 6} and S4 = {2, 4}, which of the following statements are true? (a) S1 = S2 (b) S1 = R (c) 5 ∈ S2 (d) 3 S2 (e) 4 S4 (f) S4 ⊂ R (g) S1 ⊃ S4 (h) ∅ ⊂ S2 (i) S3 ⊃ {1, 2}.
3. Which one of the following is the graph of a function (from real numbers to real numbers) drawn on a coordinate plane? (a) A circle (b) A triangle (c) A rectangle.
4. If the domain of the function f (x) = 5 + 3x − 2x2 is the set {x : 1 ≤ x ≤ 4}, find the range of the function, and express it as a set.
5. For each of the following expressions, (i) identify the largest subset D of R so that f is indeed a function from D to R; (ii) identify all vertical and horizontal asymptotes of its graph; (iii) identify where the graph intersects the horizontal and the vertical axes; (iv) identify and classify its stationary points; (v) determine its curvature; (vi) sketch its graph.
(a) f (x) = x ln(x + 1)
(b) f (x) = 3(x2 − 2x − 3)/x2
(c) f (x) = x exp(−x) + lnx
(For this one, it is enough to mark the approximate point of intersection with the horizontal axis.)
6. Find the Taylor series expansion for
f (x) = x4 + x2 + 5
centred on x = 1.
7. Let g(x) = (x − 3)(x − 2)(x − 1)
(a) Determine the values of x for which g(x) > 0, and also those for which
g(x) < 0.
(b) Expand g(x) expressing it in terms of x3 and x2 etc.
(c) Find the second order partial differentials of the function
f (x, y) = λx5 − λx4 + λx3 − 3λx2 + 117x + y2 + 2456
(d) Using the results of (a) and (b) (or otherwise) determine values of x, α and λ for which the function f (x, y) given in (c) is convex.
8. Find ∂y/∂x1 and ∂y/∂x2 , where
y = x1(2)e2x1 + 3x2 /(1 + x2 ) − 5x1(4) ln x2(2)
9. Find the total differential dy given (a) y = x1 /(x1 + x2 ) (b) y = 2x1 x2 /(x1 + x2 ).
10. Find the local (or relative) maxima and minima of y in each of the following cases: (a) y = x + 6x + 7 (b) y32 = x /3 −3x + 5x + 3 (c)32 y = 2x/(1 −2x) where x 1/2.
11. Consider the following two functions
2x − 5x2
2 + x3
and
5x2 − 2x
2 + x3
What is the relationship between the maxima and minima of these two functions? What general principle does this example illustrate?
12. Find the extreme value(s) of each of the following functions, and determine whether they are maxima or minima:
(a) y = x1(2) + x1 x2 + 2x2(2) + 3
(b) y = −x1(2) + x1 x2 − x2(2) + 2x1 + x2
(c) y = x1(2) + 3x2(2) − 3x1 x2 + 4x2 x3 + 6x3(2) .
13. Consider the function z = (x − 2)4 + (y − 3)4 .
(a) For which values of x and y does z take its minimum value?
(b) Is the first-order necessary condition for a minimum satisfied at that point?
(c) Is the second-order sufficient condition for a minimum satisfied at that point?
(d) Is the second-order necessary condition for a minimum satisfied at that point?
(e) Use the method of Lagrange multipliers to find the values of x1 and x2 that
satisfy the first-order necessary conditions for a maximum or minimum of: (a) x1 x2 subject to x1 + 2x2 = 2; (b) x1 − 3x2 − x1 x2 subject to x1 + x2 = 6.
(f) By considering small changes in the values of x1 and x2 that continue to
satisfy the constraint, determine whether these values give local maxima or minima.
(g) Find whether a slight relaxation of the constraint in the above problems will
increase or decrease the optimised value of the objective function, and at what rate.
14. Evaluate the following integrals:
(a) ∫ 2x2 e 2x dx
(b) ∫ dx
(c) ∫ (2ax + b)(ax2 + bx)7 dx
(d) dx
(e) (ax2 + bx + c)dx.
(f) ( + ) dx
(g) (x − 1)(5 − x) dx
4 Difference and Differential Equations
4.1 Prerequisites
This is an introductory course on differential equations and assumes very little prior knowledge apart from a good grounding in basic calculus.
4.2 Topics covered in the course
The idea of a differential equations - description and phase diagrams. 1st order con- stant coefficient differential equations, particular and complementary solutions. Linear approximations. Stability. 2nd order case. Transversality conditions. Difference equa- tions.
References
[1] Abadir, K.M. and J. R. Magnus. Matrix Algebra. Cambridge University Press.**
[2] Binmore, K. and J. Davies. Calculus: Concepts and Methods. Cambridge University Press.
[3] Casella, G. and R.L. Berger. Statistical Inference Duxbury Press.
[4] Greene, W.H. Econometric Analysis. Pearson.**
[5] Mas-Colell, A., M. Whinston and J. Green. Microeconomic Theory, Oxford Univer- sity Press.
[6] Miller, I. and M. Miller. John E Freund’s Mathematical Statistics with Applications Pearson.**
[7] Ostaszewski, A. Advanced Mathematical Methods. Cambridge University Press.**
[8] Pemberton, M. and N. Rau. Mathematics for Economists, Manchester University Press.
[9] Ross, S. A First Course in Probability Prentice Hall.**
[10] Sydsaeter, K. and P. Hammond. Essential Mathematics for Economic Analysis. Prentice Hall.**
[11] Wasserman,L. All of Statistics Springer.**
We are aware that library access is difficult in the current circumstances and are working to try and get electronic access to as many books and readings as possible. Books marked ** we currently have (or are negotiating for) electronic access through the Cambridge University Library. This access is only available to those with a registered @cam domain email address (these will be distributed to incoming students when their places are confirmed). You may also have access through your current University or other resources.
2022-09-26