MATH 31A (Fall quarter 2009). Honors Linear Algebra

Instructor: David A. Meyer
Office hours: AP&M 7256, WTh 1:00pm-2:00pm, or by appointment
Lecture: AP&M, room B412 (basement), MWF 9:00am-9:50am
Email: dmeyer "at" math "dot" ucsd "dot" edu

Teaching assistant: Dan Schultheis
Office hours: AP&M 5132, M 2:00pm-4:00pm, Th 9:00am-11:00am, or by appointment
Section A01: WLH, room 2209, Tu 2:00pm-2:50pm
Section A02: WLH, room 2209, Tu 3:00pm-3:50pm
Email: dschulth "at" math "dot" ucsd "dot" edu

Course description

This course is the first in the Mathematics Department's Honors sequence. It covers basic linear algebra: vectors and matrices, solution of systems of linear equations, geometry of vector spaces, linear transformations, eigenvalues and eigenvectors.

The three courses in the Honors sequence, Math 31ABC, cover essentially the same material as do Math 20F, 20C, and 20E, respectively, but at a more sophisticated conceptual level. The Honors sequence emphasizes proofs, so students completing it will be exempt from taking Math 109 (Mathematical Reasoning). The prerequisite is AP calculus in high school, with a 5 on the BC exam, or permission from the instructor. A grade of B- or better is necessary to continue from one course to the next in the sequence. The Honors sequence is intended for mathematics majors and prospective mathematics majors (although others are very welcome) and gives a much better view of what upper-division mathematics is like than does the standard Math 20 sequence.

The textbook for the whole Honors sequence is J. H. Hubbard and B. B. Hubbard, Vector Calculus, Linear Algebra, and Differential Forms: A Unified Approach, Third Edition (Ithaca, NY: Matrix Editions 2007). Errata have been compiled. In this course we will cover at least Chapter 0, sections 0, 1, 3, 4, 7; Chapter 1, sections 0—4; Chapter 2, sections 0—7. There is a copy of the textbook on reserve at the Science and Engineering library. There are many other linear algebra textbooks, most of which cover approximately the same material, at different levels of rigor and with some differences in emphasis (see, e.g., Hoffman and Kunze [1] or Strang [2]). Also, the Math Department has a calculus lab in AP&M B402A which is staffed by TAs from the Math 10 and 20 calculus sequences; they may be able to help with your questions when neither David nor Dan is available, but some of the material we cover may be outside the range of questions for which they are prepared.

There will be weekly homework assignments, due in section on Tuesdays, or before then in the drop box on the sixth floor of AP&M. Students are allowed to discuss the homework assignments among themselves, but are expected to turn in their own work — copying someone else's is not acceptable. Homework scores will constitute 1/6 of the final grade.

There will be two midterms, approximately in the fourth and eighth weeks of the quarter. The final is scheduled for 8:00am Wednesday 9 December 2009. Scores on the two midterms and final will constitute 1/4, 1/4 and 1/3 of the final grade, respectively. There will be no makeup tests.

Related events

5 Nov 09 mathematics careers seminar
AP&M B412, 4:00pm-5:00pm

Syllabus (subject to modification)

25 Sep 09 §1.0. Introduction
         overview of the course
§0.3. Set theory
         notation
         Russell's paradox [3,4,5]
§0.4. Functions
         definition
         one-to-one, onto
HWK (due Tu 29 Sep 09).
         §0.3: 1
         §0.4: 1, 2, 3, 4, 6

         [solutions]
28 Sep 09          inverse and pre-image
§1.1. Points and vectors
         positions vs. increments
                 example
         subtraction, addition and scalar multiplication
         subspaces of Rn
30 Sep 09                  examples
         the standard basis vectors
                 §0.1. Summation notation
         vector fields
                 example
§1.2. Matrices
         definition
         addition and scalar multiplication
         multiplication
HWK (due Tu 6 Oct 09).
         §1.1: 1, 4, 5, 6abch, 8
         §1.2: 2, 3, 5, 8, 10, 15, 16

         [solutions]
2 Oct 09          multiplication
                 definition
                 non-commutativity
                 associativity
                 identity matrix
         matrix inverses
5 Oct 09          matrix transpose
         symmetric, antisymmetric, triangular, diagonal matrices
         applications of matrix multiplication
                 income mobility [6,7]
                 counting paths in graphs
7 Oct 09          mathematical induction
                 Peano axioms [8]
                 examples
HWK (due Tu 13 Oct 09).
         §1.2: 17, 20, 21, *
         §1.3: 4, 8, 9, 12, 13, 18, 19, 20

         [solutions]
Extra Credit (due W 21 Oct 09).
         rounding with constraints

9 Oct 09 §1.3. Linear transformations
         definition
         linear transformations are matrix multiplications
         geometrical meaning
12 Oct 09          §0.4. Composition of functions
                 definition
         matrix multiplication as composition of linear transformations
         associativity
14 Oct 09          invertibility
§1.4. Geometry of Rn
         length
         dot product
HWK (due Tu 20 Oct 09).
         §0.4: 9, 10
         §1.4: 3, 5, 7, 8, 10, 13, 16, 19, 24, 26

         [solutions]
16 Oct 09          Schwartz' inequality
         angles
18 Oct 09
(Sunday)
review session 1:00pm-3:00pm, HSS 1128A (ground level)
(Dan's office hours on Th 22 Oct are cancelled)
19 Oct 09          invariance of dot product under rotations of R2
         geometrical meaning of determinant in 2 dimensions
         definition of determinant in 3 dimensions
         definition of cross product
         geometrical meaning of determinant in 3 dimensions
review
21 Oct 09 Midterm 1, covering §0.1, 0.3, 0.4, 1.0—1.4
23 Oct 09 Midterm 1 solutions
HWK (due Tu 27 Oct 09).
         §2.1: 2, 3, 5, 8

         [solutions]
26 Oct 09 §2.1. Row reduction
         representing systems of linear equations as Ax = b
         row operations
         échelon form
Extra Credit (due M 2 Nov 09).
         geometry of linear equations

28 Oct 09 §2.2. Solving equations
         using row reduction
                 no solutions
                 unique solution
                 infinite number of solutions
HWK (due Tu 3 Nov 09).
         §2.2: 3, 5, 7, 11
         §2.3: 2, 3, 5, 8, 12

         [solutions]
30 Oct 09          uniqueness of échelon form
         definition of pivotal column/variable
§2.3. Matrix inverses
         used to solve equations
         A is invertible implies it row reduces to I
         definition of elementary matrices
2 Nov 09          inverses of elementary matrices
         A row reduces to I implies it is invertible
         finding the inverse of a matrix
§2.4. Linear combinations, span, and linear independence
         definition of linear combination
         definition of span
         examples
4 Nov 09          definition of linear independence
                 examples
         more than n vectors in Rn are linearly dependent
         fewer than n vectors in Rn cannot span
HWK (due Tu 10 Nov 09).
         §2.4: 2, 3, 5, 7, 10, 11 (skip part c if you would have to do it by hand), 12

         [solutions]
6 Nov 09          definition of basis
         definition of orthogonal and orthonormal
         each subspace of Rn has a basis
         every basis of a subspace has the same cardinality, the dimension of the subspace
Extra Credit (due M 16 Nov 09).
         orthogonal groups

9 Nov 09 §2.5. Kernel and image
         definition of kernel and image of linear transformation
         T(x) = b has no more than 1 solution for all b iff kerT = {0}
         T(x) = b has at least 1 solution for all b iff imgT is the codomain of T
         a basis for imgT is given by the pivotal columns in [T]
HWK (due Tu 17 Nov 09).
         §2.5: 1, 2, 3, 5, 6, 8, 9, 10, 15 18

         [solutions]
11 Nov 09 no lecture, Veterans Day holiday [9,10]
13 Nov 09          finding a basis for kerT
         for any linear transformation T :RnRm, dim kerT + dim imgT = n
         rankT = dim imgT, nullityT = dim kerT
         for any matrix A, rankA = rankAT
         polynomial interpolation
                 define T :{polymomials of degree k} → Rk+1 by T(p) = [p(0),p(1),...,p(k)]
                 T is a linear transformation
15 Nov 09
(Sunday)
review session 1:00pm-3:00pm, HSS 1128A (ground level)
practice midterm
16 Nov 09                  kerT = {0}, so T -1 exists
                 calculation of T -1 for k = 2
review
18 Nov 09 Midterm 2, covering §2.0—2.5
20 Nov 09
Dan
Midterm 2 solutions
23 Nov 09 §2.6. Abstract vector spaces
         definition of real vector space
         definition of linear transformation, isomorphism
         example of a vector space, continuous functions on [0,1], not isomorphic to Rn
HWK (due Tu 1 Dec 09).
         §2.6: 1, 2, 4, 5, 7, 8, 10, 11

25 Nov 09          definition of linear combination, span, linear independence, basis
         definition of the concrete-to-abstract function
         derivation of the change-of-basis function
27 Nov 09 no lecture, Thanksgiving holiday
30 Nov 09 §2.7. Eigenvalues and eigenvectors
         Fibonnaci numbers example
                 raising a matrix to a power
         definition of eigenvalue and eigenvector
         a matrix is diagonalizable iff a matrix of its eigenvectors is invertible
2 Dec 09          eigenvectors with distinct eigenvalues are linearly independent
         finding eigenvalues and eigenvectors of a matrix
Suggested problems.
         §2.7: 1, 2, 3, 6

4 Dec 09 §2.7. Eigenvalues and eigenvectors

Suggested reading

[1] K. M. Hoffman and R. Kunze, Linear Algebra, Second edition (Englewood Cliffs, NJ: Prentice Hall 1971).
[2] G. Strang, Introduction to Linear Algebra, Fourth edition (Wellesley, MA: Wellesley-Cambridge Press 2009).
[3] B. Russell, "Letter to Frege" (1902), in J. van Heijenoort, From Frege to Gödel: A Source Book in Mathematical Logic, 1879-1931 (Cambridge, MA: Harvard University Press 1967) 124-125.
[4] A. D. Irvine, "Russell's paradox", in E. N. Zalta, Principal Editor, Stanford Encyclopedia of Philosophy (2009).
[5] A. Doxiadis and C. H. Papadimitriou, art by A. Papadatos and A. Di Donna, Logicomix: An Epic Search for Truth (New York: Bloomsbury USA 2009).
[6] T. Hertz, "Understanding mobility in America", Center for American Progress report (2006).
[7] J. B. Isaacs, "Economic mobility of families across generations", Pew Charitable Trusts report (2007).
[8] D. R. Hofstadter, Gödel, Escher, Bach: an Eternal Golden Braid (New York: Basic Books 1979).
[9] M. Cleland, "The forever war of the mind", New York Times, 6 November 2009.
[10] C. Alexander, "Back from the war, but not really home", New York Times, 7 November 2009.

Last modified: 2 Dec 09.