# Math 225 Linear Algebra and Matrix Theory

## Semester: Spring 2014

Lecture 01 (20259)
 Inst : Dr. Asher Auel asher * auel AT yale * edu Time : Tue Thu 09:00 - 10:15 am Loct : LOM 215 (ROOM CHANGE)
 Office : LOM 210 Phone : (203) 432-4187 Officehours : Mon 2:30 - 3:30 pm Tue 1:30 - 2:30 pm
 Text : Linear Algebra, 4th Edition Stephen H. Friedberg, Arnold J. Insel, Lawrence E. Spence Pearson, 2003. ISBN-10: 0-13-008451-4. ISBN-13: 978-0130084514.
Course syllabus and homework schedule.
 Teaching Fellow : Max Ehrman Recitation Time : Mon 4:30 - 6:00 pm Recitation Loct : LOM 214

Description of course: Linear Algebra can be regarded as the art of solving linear equations. You have seen such equations since middle school: if 2x=4 then find x. In high school, you probably solved some systems of 2 or 3 simultaneous linear equations in 2 or 3 variables. Such systems can be organized into a matrix equation Ax=b, where A is a matrix, x is a variable vector, and b is a constant vector. Linear algebra is a deep investigation into systems of simultaneous linear equations. In the course, we will examine such questions as: How do we know when a system of m linear equations in n variables has a solution? How many solutions can there be? How do we find them efficiently? If there is no solution, then how close can we get to one? While such questions might seem somewhat abstract, they are actually fundamental to the natural sciences, computer science, economics, and statistics. Furthermore, almost all higher mathematics today (geometry, topology, number theory, analysis, differential equations, etc.) depends on linear algebra in some fundamental way.

The main topics covered will be vector spaces, linear transformations, matrices, systems of linear equations, determinants, eigenvalues, eigenvectors, diagonalization, and applications. Time permitting, we will investigate the theory of Markov chains and the linear algebra behind Google's PageRank algorithm. Math 225 (as opposed to Math 222) is more focused on the abstract aspects of linear algebra and will demand a fair amount of maturity of mathematical thinking, not just rote problem solving. The course will try to strike a balance between computations, concepts, proofs, and applications. Some short proofs may appear on homework assignments and exams.

Expected background: Officially, the prerequisite is Math 120 (taken earlier or concurrently). In reality, we will hardly use any calculus. However, it is important that you are comfortable with vectors and basic geometry of 3-dimensional space as taught in Math 120 (e.g., vector addition, scalar multiplication, dot product, magnitude, normal vectors, lines and planes in three dimensional space).

 Homework 20% Midterm exam 1 (13 Feb) 25% Midterm exam 2 (01 Apr) 25% Final exam (01 May) 30%
Grades: Your final grade will be based on weekly homework, two midterm exams, and a final exam. Notice that more emphasis is placed on exams than on weekly homework assignments in computing your final grade. On the other hand, completing your weekly homework will be crucial to your success on the exams.
Group work, honestly: Working with other people on mathematics is highly encouraged and fun. You may work with anyone (e.g., other students in your section, in the course, not in the course, tutors, bums on the street, ...) on your homework problems. If done right, you'll learn the material better and more efficiently working in groups. The golden rule is:
Work with anyone on solving your homework problems,
but write up your final draft by yourself.
Writing up the final draft is as important a process as figuring out the problems on scratch paper with your friends, see the guidelines below. Mathematical writing is very idiosyncratic - we will be able to tell if papers have been copied - just don't do it! You will not learn by copying solutions from others or from the internet! Also, if you work with people on a particular assignment, you must list your collaborators on the top of the first page. This makes the process fun, transparent, and honest.

# Policies

(or otherwise the small print)

Homework: Weekly homework will be due to my departmental mailbox by 4 pm each Wednesday. Each assignment will be posted on the syllabus page the week before it's due.

Late or improperly submitted homework will not be accepted. If you know in advance that you will be unable to submit your homework at the correct time and place, you must make special arrangements ahead of time. Under extraordinary circumstances, late homework may be accepted with a dean's excuse.

Consider the pieces of paper you turn in as a final copy: written neatly and straight across the page, on clean paper, with nice margins and lots of space, and well organized.

No homework will be due during the two weeks of the midterm exams.

Your lowest homework score from the semester will be dropped.

Exams/quizzes: The two midterm exams will take place during lecture on Thursday February 14th and Tuesday April 1st. The final exam will be take place 09:00 am - 12:30 pm on Thursday, May 1st, 2014 in a location to be decided by the registrar.

Make-up exams will only be allowed with a dean's excuse and must be arranged in advance.

The use of electronic devices of any kind during exams is strictly forbidden.

Homework guidelines: Generally, a homework problem in any math course will consist of two parts: the creative part and the write-up.

• The creative part: This is when you "solve" the problem. You stare at it, poke at it, and work on it until you understand what's being asked, and then try different ideas until you find something that works. This part is fun to do with your friends; you can do it on the back of a napkin. If you're having trouble, even in understanding what the problem's asking, use the resources available to you: my office hours, teaching assistants' office hours, weekly tutoring sessions, etc. Ask for help as early as you can! This part should all be done on "scratch paper."

• The write-up: Now that everything about the problem is clear in your mind, you go off by yourself and write up a coherent, succinct, and nicely written solution on clean sheets of paper. Consider this your final draft, just as in any other course. This part you should definitely NOT do with your friends.