21-260 Differential Equations

Final Grades

2007-05-15T14:54:00.000-05:00

Well, the exams have been graded and final grades have been submitted.

The grade cutoffs for the final exam are the standard array: 85-75-65-50. Averaging the cutoffs for all the assignments this semester yields final average cutoffs of: 82-72-62-48. When computing your final averages, I fudged a little bit in your favor, shifting some weight to your mid-term exam average or your final exam grade, depending on which was higher. This caused a few of you who were very close to a cutoff to receive the higher grade. This affected about 4%-5% of the class.

Once I get the statistics sheet of my spreadsheet cleaned up a little, I'll post the final version. That will probably happen tomorrow morning.

Homework #15 Grades

2007-05-11T07:50:00.000-05:00

I've been fielding quite a few questions along the lines of "I see that there is an average score for HW#15, but I don't have a grade recorded. Did my homework get lost?" I just want to assure you that only a small number of the HW#15 grades have been recorded. (One or two sections, maybe.) So you should not be alarmed by this.

The TA's all have final exams and projects as well, and some have been getting their grading done early, while others have been waiting until after their exams early this week. I hope to have all the grades assigned and submitted on Monday or Tuesday next week.

Two Final Announcements

2007-05-06T10:23:00.000-05:00

Solutions to the last homwork asignment (HW#15) are now available outside my office door.
At yesterday's review session, I was asked what you will need to know about the matemtaical models we studied using first order differential equations. I could think of four main things Newton's Law of Eooling and the exponential growth and decay models. You should have these memorized (i.e. the differential equations, method of solution, and applications). You should be able to recognize a logistic growth model, and be able to come up with the differential equation with some prompting. You should not memorize Torricelli's law.

One Last Chance

2007-05-05T14:24:00.000-05:00

I'll be in my office for about an hour on Sunday, from 11:30-12:30. IF you have any last questions you would like answered, I'll try to do so.

Final Exam Review Session

2007-05-04T18:24:00.000-05:00

I'll hold a review session for the final exam tomorrow, May 6, from 1:00-2:30pm in DH 2315. Bring your questions!

Change in office hours, sections F and G

2007-04-29T21:13:00.000-05:00

I'll be away for Tuesday and Wednesday so I'll have to cancel my office hours. So instead I'll have an office-hours-marathon on Sunday from 4:00 to 7:00.

The Final Exam Review Page

2007-04-28T09:05:00.000-05:00

has been posted.

Note that the final exam is a cumulative exam, thought the material that was not covered on the three midterm exams may receive some emphasis.

Assignment for Week #15

2007-04-28T09:01:00.000-05:00

I've posted the reading and homework for Week #15. Follow the link from the schedule page.

Homework #15 is due on the last day of class. Our final exam follows hot on it's heels -- First thing Monday morning. I don't know that the homework can be graded by then, but I will make sure that solutions to HW#15 are available over the weekend. Because of this, I will not be able to accept late homework for this last assignment.

Final Exam

2007-04-24T09:12:00.000-05:00

Our final exam is scheduled for Monday morning, May 7, from 8:30-11:30am. Some of you may have conflicts with this time, either another exam scheduled at the same time (I still don't understand why this happens) or three exams starting within a 25 hour time period. I'll hold an alternate exam on Thursday May 10, from 8:30-11:30am for these students.

If you wish to take the alternate exam, you will need to let me know in advance. You should also provide documentation of your conflict. (e.g. a printout of your course schedule with the conflicting courses highlighted).

Cumulative Averages

2007-04-17T15:52:00.000-05:00

I know that many of you are reviewing your grades and looking ahead to the final exam. You may be wondering just where you stand in the course. With that in mind, I just looked at the "Weighted Total" column in the Blackboard gradebook. I spot checked about 5 entries, and they agree with the averages I have computed in my spreadsheet. They all matched up, so I am concluding that Blackboard is calculating grades the same way I am. I am pleased by this, since Blackboard is the most cumbersome and non-intuitive application I have used in a long time. I would hate to have to change anything.

In order to see where you stand in the course, you can look at your Weighted Total and compare it to the grade cutoffs in the "Cumulative Average" section of the Statistics page.

One word of warning. If you have turned in late homeworks, the Weighted Total will be off by some amount. If you've only turned in one late assignment the Weighted Total will be high by .01% or so. If you've turned in more than that it will be off by a greater amount. Any grade that is not an integer has been recorded as a late grade.

Assignment for Week #13

2007-04-17T09:01:00.000-05:00

Well, I was looking at the state of our course, what we've covered recently and our schedule this week. I had initially intended to assign homework due Wednesday this week. Since I cancelled class that day, compensating for our early morning exam, that doesn't seem to make much sense. Monday is the next possible day, but that is right after carnival. I could make the assignment due a week from Wednesday, but then would I have another assignment due two days later?

Ultimately, I decided that there will be no homework assignment for this week. I'll just lump this week's and next week's assignment together and make it all due a week from Friday, i.e. April 27. It will be a bit longer than usual, so you may want to start on it earlier than usual.

SYNOPSIS: No homework this week. Long assignment due next week. Enjoy Carnival. Start your homework early.

Exam #3 Wrapup

2007-04-17T08:56:00.000-05:00

I've updated the statistics for the course to include the results of Exam #3.

One other thing: I passed out the exams in class yesterday. If you accidentely pick up an exam that was not yours, could you bring it back to me. The person it belongs to would certainly like to have it.

Exam #3

2007-04-06T14:52:00.000-05:00

I've posted a review page for Exam #3, which will be held next Friday, April 13, from 7:30-8:20am in UC McConomy. You can find the link on the schedule page. I'll update it with old exam problems when I get a chance.

UPDATE: I've added some old exam problems to the review page.

UPDATE: I will hold a review session tonight from 6:30-8:00 in DH 2210. You can ask whatever questions you may have then.

Exam #2 Wrapup

2007-04-02T18:59:00.001-05:00

I've updated the Statistics to include the results of Exam #2. You can you can use this page to gauge your standing in the course.

I'll get solutions for Exam #2 to your TA's so they can be distributed during recitations on Thursday.

Incidentally, I am frequently asked, "What do the letter grade cutoffs mean for my final grade?" or words to that effect. To get the cutoffs for final grades, the A cutoff for example, I simply average the A cutoffs for each assignment, just like I average your grades. You can see the current grade cutoffs in the top section, labeled "Cumulative Average."

Assignment for Week #11

2007-04-02T18:56:00.000-05:00

The assignment for Week #11 has been posted. You can find a link on the Schedule page of the Course Website.

Exam #3

2007-03-28T17:26:00.000-05:00

I guess the resolution of this post was somewhat ambiguous. Let me clarify matters: Exam #3 will be held on Friday, April 13 in McConomy Auditorium at 7:30am. This is one week before Spring Carnival.

Assignment for Week #10

2007-03-28T17:21:00.000-05:00

The assignment for Week #10 is available. You can follow the link from the Schedule Page of the course course website.

Just to be clear, in problems 3.1.4, 3.4.12 and 3.5.4, where you are instructed to convert the second order equation to a system, you should find the solution by first solving the system and reading off the solution to the second order equation from that.

Exam #2

2007-03-17T14:23:00.000-05:00

Exam #2 will take place on Wednesday, March 21. The exam will be held during the normal class times, 10:30-11:20 or 12:30-1:20. The exam will not be in the usual classrooms, however. They will be held in McConomy Auditorium.

There is a review page posted on the 21-260 website. The exam covers Chapter 7 in the text (Systems of differential equations). The specific sections, as well as review problems from the text are listed on the review page. The review page also provides some exam questions I've posed to my 21-260 students in previous semesters. Note that soltuions to the old exam problems will not be distributed. You have lots of problems with solutions available in the textbook, and I think it is important for you to get used to working through problems without having the solution available as a reference. You are certainly welcome to ask your TA or me about these problems.

I will hold a review session on Monday evening, from 6:30-8:00pm in DH 2210. That will be a good opportunity to ask questions about the old exam problems.

Back to Work

2007-03-16T08:16:00.000-05:00

Well, I'm back from my trip. I'll be catching up on my email this morning. If you've been waiting to hear from me, I should get back to you sometime today.

Today, I will also post some old exam problems on the Exam #2 Review Page, I'll also try to get you some more information about an Exam #2 Review Session, which I'll try to schedule for Monday evening.

Spring Break 2

2007-03-07T23:32:00.000-05:00

Well, the weather situation seems to be looking a bit better. In New England, though, you can never tell. There's still a chance I could end up with this:

Recitation for March 7

2007-03-07T23:30:00.000-05:00

Tomorrow in Recitation your TA's should have solutions to Exam #1 available, as well as most of the exams submitted for regrades. A few that were submitted later than the others are not done yet.

Spring Break

2007-03-06T19:57:00.000-05:00

Before class yesterday I shared with you my plans for spring break. I also mentioned some anxiety I have about those plans.

Well, here is what I'm hoping for:

Click the image for a full sized picture.

Assignment for Week #8

2007-03-06T19:35:00.000-05:00

I'm noticing that I never posted a note here for the homework assignment for Week #8. Well here it is. You can find a link to the assignment from the Schedule page of the Course Website.

I notice that a few people have posted homework questions under the "Borrowed Pencil" post. You can ask any other questions you have in comments to this post.

Borrowed Pencil

2007-03-01T18:12:00.000-05:00

I borrowed somebody's pencil in secion G and forgot to return it. If you cannot survive without your precious mechanical pencil, send me an email and I'll get it back to you. Otherwise I'll bring it to recitation next week.

Problem Contest

2007-02-26T20:27:00.000-05:00

Last Friday, I started class with an announcement of a problem solving contest. If you are interested in participating, you can go to the Spring Problem Solving Contest website for more information.

Office Hours for Tuesday 2/27

2007-02-25T14:38:00.002-05:00

I haven't been very good about posting to the blog lately, but I'll try to keep up with it more. How's this: I'm going to have to move my office hours on Tuesday to later in the day. Rather than 10:30am-12:20pm, I'll plan to hold them from 4:00pm to 6:00pm.

Assignment for Week #7

2007-02-25T14:38:00.001-05:00

I posted the assignment for Week #7 on Friday afternoon, but I didn't get a chance to post about it here until now. You can find it by following the link from the Schedule page. There are a couple "home-made" additional problems that I will add on Monday afternoon.

UPDATE: I've added the additional problems to the homework page for Week #7. Try refreshing your browser if they don't show up.

UPDATE: In problem 7.4.2, you should skip part (d). Do only parts (a), (b) and (c).

Assignment for Week #6

2007-02-17T09:05:00.000-05:00

There will be a homework assignment for Week #6, but it's likely I won't get to post it until Monday, or maybe Sunday evening. If you are anxious to get started, you can be sure that the problems 7.3.6 and 7.3.10 will be on it. You can get to work on those.

UPDATE: The assignment has been posted. It does, indeed, include 7.3.6 and 7.3.10. You can follow the link from the Schedule Page to find out the other problems.

Sections A and B

2007-02-13T14:18:00.000-05:00

In case any of you cannot make it to the office hours today, you can collect your homework and solutions from outside my office. Homeworks 1 to 4 of each section are in a box and you can also find solutions to all the assignments. My office is WeH 7215.

mistakes hw 4

2007-02-12T17:52:00.000-05:00

In the set of solutions that I wrote to hw 4 there are two mistakes, but I don't want to waste paper and print new copies of the solutions, so I'll just post here the corrections. 1 In exercise number 7.2.1 part d the element in the second raw and first column should be 14, not 7 as I wrote. 2 In the first additional exercise part b all the directions that I draw should be rotated counterclockwise by 90 degrees. So for example for R bigger then 4 and F bigger then 1.5 the answer would be Up Left instead of Up Right etc.

Exam #1 Review Session

2007-02-12T12:08:00.000-05:00

I'll be holding a review session tonight, from 8:00-9:30pm. It will be held in DH 2315. This will be a good chance for you to ask questions about the review problems.

Office Hours before exam

2007-02-09T12:49:00.000-05:00

Because of the exam next Wednesday I'll hold office hours on Monday from 5:00 to 6:00 instead of Wednesday. The Tuesday office hours are unchanged, from 3:30 to 5:00. For those of you who don't know where the Physical Plant Building is, here are the directions. If you can't make it to office hours, you can pick up all old homeworks and solutions in a box outside my office, after the Monday office hours.

changed office hours

2007-02-09T09:32:00.000-05:00

Just for the next week I'll have office hours on Monday from 5 to 7 pm instead of Thursday from 10:30 to noon, so you can come to pick up your graded homeworks with the solutions. I'll have as usual office hours on Monday from 10:30 to noon as well, but I cannot give you the hws and the solutions at that time.

Turning in Late Homework

2007-02-05T15:42:00.000-05:00

According to the policy set out on the Grading Page of the 21-260 Website, I accept late homework until the solutions are distributed. This typically happens during recitation six days after the due date.

Since Exam #1 will be held next Wednesday (You remembered Exam #1, right -- more on that later) graded homework and homework solutions will be distributed starting Monday afternoon. If you plan to turn in late homework, as some athletes do this week, you must turn it in to me by 1:20. You can give it to me during lecture, or put it in my mailbox.

How About a Cell Phone?

2007-02-05T15:36:00.000-05:00

Someone left a cell phone in WEH 7500 after today's 12:30 lecture. If you are missing your phone, let me know. I'll hold onto it for a few days and if no one comes to claim it I'll ~~sell it on ebay~~ leave it with the information desk at the University Center.

Missing a Calculator?

2007-02-04T21:28:00.000-05:00

I received this email from a student last week.

I am in Graph Theory in A51 after your class. A student left a calculator on (TI-83) one of the tables. If anybody asks, it has been turned into the UC info desk lost-and-found.

If you are missing a calculator, this may be yours.

Assignment for Week #4

2007-02-02T15:20:00.000-05:00

The reading and homework for Week #4 have been posted. Follow the link from the Schedule Page of the course website.

UPDATE: You should feel free to use the program pplane wherever you are asked to sketch direction fields in a phase plane, or produce sketches of solution curves in the phase plane.

UPDATE: We did not get to cover linear independence of vectors this week, so I have removed problems 7.3.6 and 7.3.10 from the assignment. They will return on the next assignment, after next week's exam.

UPDATE: There is one other bit of information that will help with problem 7.2.22: If you have a matrix (or a vector) with entries that depend on t, then to differentiate that matrix (or vector) you simply differentiate each component separately.

For example the derivative, with respect to t, of [f(t) g(t)] is

[(df/dt) (dg/dt)].

I've asked your TA's to comment on this in tomorrows recitation.

Move Exam #3?

2007-02-01T11:55:00.000-05:00

It has come to my attention that the Wednesday before Spring Carnival is an unpopular time to hold an exam.

It seems that it may be possible to move the exam to the preceeding Friday (Friday, April 13). Unfortunatly, there is nothing to be done about the whole 7:30 in the morning business. Unless I hear strong complaints about this change over the next few days, I will move the exam.

UPDATE: I will move Exam #3 to Friday, April 13.

The Blackboard Site is Available

2007-02-01T11:13:00.000-05:00

I've made the Blackboard site available. It looks like all the grades for HW#1 have been recorded, as well as some grades for HW#2. For news and information about the course, you should check the course website, or this Blog. I'll try to keep them both updated. The Blackboard site will mainly be there for you to check your grades.

Assignment for Week #3

2007-01-27T14:32:00.000-05:00

The reading and homework for Week #2 have been posted. Follow the link from the Schedule Page of the course website.

There are a couple "homemade" problems this week. They are available in a pdf file linked from the assignment page. You only need to complete the first two (this week). Early next week I'll post a new pdf file with only those problems you need to complete.

UPDATE: For problem 2.3.15 you will want to use dfield, or some other technology. You will find it quite difficult to complete the integration by hand. Additionally, problem 2.5.7(b) makes some comments about the phase line for the differential equation in question. You should actually show the phase line in your solution. Problem 2.5.20(b) is also simplified greatly by looking at the phase line, though it is not, strictly speaking, necessary.

Problem 2.3.8

2007-01-26T07:58:00.000-05:00

I've been asked to comment on problem 2.3.8, in which you are asked to find the rate of return required for an investment of $2000 per year to grow to $1,000,000 over the course of 40 years. To complete this problem, as noted by commenter "anonymous" to this post, you must solve an equation of the form (e^(rt)-1)/r=[constant].

I didn't remark on this earlier, because I though commenter Jeffrey addresses the situation adequately. You will have to find some way to solve this numerically. If your calculator has a "solver" you can use that. Another method would be to graph the function f(r)=(e^(rt)-1)/r-[constant] and determine (by inspection) where it crosses the x-axis. Newton's method could, in principle, be employed, but it gets unwieldy rather quickly.

Sections A & B

2007-01-25T10:37:00.000-05:00

Some of you have not collected your graded homework from last week and/or solutions of Homework 1 . Please stop by my office to collect these. I won't be carrying them to class next week.

Office Hours for Dr. Handron

2007-01-22T17:58:00.000-05:00

This semester, starting tomorrow, I'll hold regular office hours on Tuesdays, from 10:30-12:20, and on Wednesdays, from 1:30-3:20. I'll be in my office during those times, and you can see me to discuss any aspect of the course (homework, previous grades, etc.)

Assignment for Week #2

2007-01-20T09:58:00.000-05:00

The reading and homework for Week #2 have been posted. Follow the link from the Schedule Page of the course website.

A number of the problems will require you to use some sort of computer technology. I would recommend the Java applet dfield, which I will be demonstrating in class on Monday and/or Wednesday.

UPDATE: I've made a slight modification to the homework exercises for Week #2. I've removed 1.1.27 and 2.1.15 from the assignment, and added 1.2.16, 2.3.4 and 2.3.8.

UPDATE: I've also removed 2.2.22, and added 2.3.6.

Office Hours for sections F and G

2007-01-19T17:41:00.000-05:00

Office hours for Sections F and G are Tuesdays 3:30 to 5:00 and Wednesdays 1:00 to 2:00. My office is in the Physical Plant Building, please follow the directions to find it.

Information for Sections A & B

2007-01-18T21:27:00.000-05:00

My office is WeH 7215. It was listed incorrectly on the course website. My office hours are Tuesdays 1:30 p.m. to 3 p.m. and Thursdays 11 a.m. to 12:30 p.m.

Our Textbook is Sold Out

2007-01-18T11:16:00.000-05:00

I have heard from a few students that the CMU Bookstore has run out of our textbook. You may all rest assured that I have anticipated just such an occurrence. The homework problems are conveniently available as a pdf file. I won't do that every week, but I know this is a common problem in the first week.

Incidentally, if you are sans textbook, and would like a reference while you complete the homework, you can use the lecture notes I posted earlier.

Textbooks, Old and New

2007-01-18T08:50:00.000-05:00

Some students have asked about using the 7th edition of our textbook, rather than the current 8th edition. To my knowledge, there are no major changes to the text. There are a few changes, though. If you plan to use the 7th edition, you will want to pay careful attention to the exercises, or you might end up doing the wrong problems.

For instance, this week, the problems 1.3.2, 1.3.10, and 1.3.27 are the same. The 7th edition does not have a problem 1.3.30, though.

If you do decide to get by with the 7th edition, you will be responsible for making sure you do the correct problems. If you fail to do so, and points are deducted, well... don't come cryin' ta me.

Office Hours for Week #1

2007-01-17T13:35:00.000-05:00

I'll hold office hours tomorrow (Thursday) from 1:30-3:20. At the start of next week I'll announce my regular office hours for the semester.

Class Schedule for Wednesday

2007-01-16T10:32:00.000-05:00

Since Lecture 2 (12:30) did not meet on Monday, due to the half-holiday, I'm going to cancel the 10:30 (Lecture 1) lecture on Wednesday. This will make sure that the two lectures stay on the same schedule.

I announced this at the end of class yesterday, but I want to make sure the word gets out.

Assignment for Week #1

2007-01-14T12:27:00.000-05:00

The reading and homework assignments for Week #1 have been posted. Follow the link from the Schedule Page of the course website. You will have to take a short tour of the Policies page before you can view the Exercises.

The assignment for this week should not be especially strenuous. If you have any questions or concerns, though, I encourage you to post a comment under this entry. Your TA's and I will try to review the comments and respond as needed. Probably not at 2:00am, though.

Alternatively, if you see a question you feel like answering, you can go ahead and do that too.

UPDATE: I've corrected the pdf file to correct the typo in problem 1.3.2. I've also corrected the due date in the pdf file: Friday 19 January.

Lecture Notes for Weeks #1 and #2

2007-01-12T14:19:00.000-05:00

During the first few weeks of the semester we will be jumping aroung in the textbook quite a bit. In order to give a more coherent presentation, I've written up these notes. They are definitely "rough around the edges," but I think they will be useful, especially to read over after attending the lectures.

UPDATE: I've corrected the link to the notes. They should download correctly now.

Welcome to the 21-260 Blog

2006-11-30T09:48:00.000-05:00

I'm setting up this blog as a way to foster communication in 21-260 Differential Equations. The idea is for myself and the TA's to have posting priveleges, and allow studetns to make comments. Check back for updates later.