Math 2135
Linear Algebra


Fall 2021

Please see below for lecture summaries, homework and other study material. For your grades, please see Canvas.

Date Topics
Aug.23. Matrix encodings of linear systems. Elementary row operations on matrices. Notes.
Aug.25. Echelon and reduced echelon forms. Examples of row reduction. Notes.
HW1 (due Wed. Sep.01.): 1.1: 4, 12, 16, 20, 22, 24; 1.2: 2, 8, 10, 16, 18.
Aug.27. The Gaussian elimination algorithm. Pivots. Notes.
Aug.30. Existence and uniqueness of solutions for linear systems via Echelon forms. Notes.
Sep.01. Matrix-vector products. Linear systems as vector equations and matrix equations. Notes.
HW2 (due Wed. Sep.08.): 1.3: 2, 6, 10, 14, 16, 21, 22, 24, 26.
Sep.03. Spans and spanning sets. Notes.
Sep.06. Labor day; no class.
Sep.08. Proof of echelon form criterion for spanning sets. Linear independence. Notes.
HW3 (due Wed. Sep.15.): 1.4: 8, 10, 13, 14, 15, 22, 25, 26; 1.5: 16, 18.
Sep.10. More criteria for linear independence, with proofs. Geometry of R^2 and R^3. Notes.
Sep.13. The parallellogram law. Solution sets of homogeneous vs. nonhomogeneous equations. Notes.
Sep.15. Linear transformations: definition, properties, and examples. Notes.
HW4 (due Wed. Sep.22.): 1.5: 25, 26; 1.7: 4, 14, 16, 18, 20; 1.8: 10, 17, 20.
Sep.17. Relationship between linear maps and matrix multiplications. Image, kernel, surjectivity and injectivity of linear maps. Notes.
Midterm I date announced: Friday, October 1 (in class).
Sep.20. Image, surjectivity, and spans; kernel, injectivity and linear independence. Some geometric transformations in R^2. Notes.
Sep.22. More geometric transformations. Addition, scaling and multiplication of matrices. Notes.
HW5 (due Wed. Sep.29.): 1.9: 4, 6, 8, 10, 12; 2.1: 2, 9, 10.
Sep.24. Properties and "non-properties" of matrix operations. Notes. Review for Midterm I.
Sep.27. Matrix multiplication vs. composition of linear maps. Proof of associativity for matrix multplication. Definition of invertible matrix. Notes.
Sep.29. Inversion and cancellation. Inverses of 2*2 matrices. Powers and transposes of matrices. Midterm questions. Notes. (No homework is due next Wednesday.)
Oct.01. Midterm I.
Oct.04. More properties of inversion. Algorithm for tesing invertibility and finding inverses. Notes.
Oct.06. Example computations of matrix inverses. The invertibility theorem. Notes.
HW6 (due Wed. Oct.13.): 2.1: 11, 18; 2.2: 4, 7, 25, 32; 2.3: 4, 6, 17, 18, 33, 34.
Oct.08. Invertible linear maps. Subspaces of R^n. Notes.
Oct.11. More examples of subspaces of R^n (with proofs). Notes.
Oct.13. Bases and dimension: definition and first examples. Notes.
HW7 (due Wed. Oct.20.): 2.8: 2, 6, 12, 16, 18; 2.9: 2, 4, 8, 10, 14.
Oct.15. Basis and unique decomposition. Bases and dimensions of the column, row and null spaces of matrices. Notes.
Oct.18. Decomposition vectors. More bases computations. The rank-nullity theorem. Notes.
Oct.20. Computation of determinants via cofactor expansions. Notes.
HW8 (due Wed. Oct.27.): 3.1: 4, 10, 14, 20, 24, 34, 36; 3.2: 16, 18, 20, 22, 24.
Oct.22. Properties of determinants. Notes.
Oct.25. New determinants from old. Applications of determinants. Notes.
Oct.27. Determinants as area/volume. Definition and examples of abstract vector spaces. Notes.
HW9 (due Wed. Nov.3.): 3.3: 20, 22; 4.1: 2, 6, 8, 12, 16, 18, 26, 28.
Oct.29. Working with vector space axioms. Linear combinations. Subspaces. Notes.
Midterm II date announced: Friday, November 12 (in class).
Nov.01. Old to new: generalizing familiar notions/facts from R^n to abstract vector spaces. Notes. Proof worksheet.
Nov.03. New to old: solving problems about abstract vector spaces using R^n via coordinate mappings. Notes. Review for Midterm II.
HW10 (due Wed. Nov.10.): 4.2: 2, 4, 8, 10, 14; 4.4: 2, 8, 12, 14, 28, 32; 4.5: 12, 14.
Nov.05. Going over Homework 10, the proof worksheet, and the midterm review. Notes.
Nov.08. Change-of-basis matrices: definition and properties. Notes. Solutions to review for Midterm II.
Nov.10. Computation of change-of-basis matrices. Matrices of linear maps. Notes. (No homework is due next Wednesday.)
Nov.12. Midterm II.
Nov.15. Motivation for diagonalization. Definition of eigenvalues and eigenvectors. Characteristic polynomials. Notes.
Nov.17. Computation of eigenvalues and eigenvetors. Notes.
HW11 (due Wed. Dec.1.): 5.1: 2, 6, 10, 14; 5.2: 4, 10; 5.3: 2, 10, 12, 14.
Nov.19. The diagonalizability theorem. Notes.
Nov.22. Winter Break Week; no class.
Nov.29. Diagonalization examples. Explanation for the equality "A=PDP^{-1}". Notes.
Dec.01. More on "A=PDP^{-1}". Complex eigenvalues. Definition of inner products. Notes.
HW12 (due Wed. Dec.8.): 5.4: 2, 6, 14, 16; 6.1: 2, 6, 8, 10, 13, 14.
Dec.03. Properties of inner products. Geometric notions arising from inner products. Notes.
Dec.06. Orthogonal sets and bases. Notes.
Dec.08. Orthogonal projections. The Gram--Schmidt process. Notes. Review for Chapters 5 & 6.
HW13 (do not hand in): 6.2: 2, 4, 8, 10, 12, 14; 6.3: 2, 6, 8, 10, 12, 16.
Dec.14. Final Exam, from 4:30 to 7:00 pm.