Being a weblog devoted to a variety of topics. Including Mathematics. And Mathematical Finance. Sometimes with homework.

Sunday, August 31, 2008

21-260: Assignment for Week #2

The reading and homework assignment for Week #2 has been posted. As before, if you have questions or concerns related to the homework, feel free to post them in the comments.

UPDATE: For some of the problems you will want to use the "dfield" program that I showed to you in class on Friday. I neglected to post the link to it earlier, but here it is now.

Wednesday, August 27, 2008

xkcd and set theory


21-260: Lecture Notes

During the first few weeks of the semester we will be jumping around 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.

Tuesday, August 26, 2008

Engines of Our Ingenuity: The Pigeonhole Principle

A recent episode of Engines of Our Ingenuity discusses the Pigeonhole Principle. I've mentioned Engines of Our Ingenuity before. If you find these episodes interesting, you can search the entire list of episodes (each tagged with keywords).

Monday, August 25, 2008

21-260: Assignment for Week #1

I've posted the reading and homework assignments for Week #1.

If you have questions or comments about the assignment, feel free to post them in the comments. Either I or one of your TA's (or a fellow student) may be able to answer your question. The comments are not a substitute for office hours, but may be a good way to deal with some issues...

UPDATE: A few of you, having ordered your textbook online only to have it arrive late, have prevailed upon me to post the week's homework problems. Being good natured and generally accommodating, here they are.

Sunday, August 24, 2008

Welcome to 21-260

Welcome to 21-260 Differential Equations. I'll use this blog to post information and updates about the course. See you in class on Monday.

Friday, August 15, 2008

Vynyl LP's to MP3's

In the olden days, we used to listen to music on vinyl LP records. Nowadays, though, it is much more convenient to listen to music in a digital format. Accordingly, those of us of a certain age are faced with a problem: what to do about that record collection.

During the 1980's, I accumulated a pretty sizable record collection. When CD's were released in the late 80's, I started buying music in that format. I got CD duplicates of many of my most favorite albums. But a lot of others slipped through the cracks.

It is possible to buy turntables designed to connect directly to your computer in order record your music and save it in your desired format. But if you have enough LP's to make this worthwhile you probably already have a turntable. It seems like a waste to buy a new one. In fact it is.

I've had great success ripping my LP's using only: (1) My stereo, specifically a Techniques turntable and amplifier purchased sometime before 1988, (2) a MacBook Pro, and (3) the free application Audacity (If you want to create MP3's, you'll also need the LAME MP3 encoder, also free.) Oh, also (4) a "two RCA to mini-stereo" cable.

Once you've downloaded the software, connect the mini-stereo end of your cable to the "audio in" on your computer. Then connect the RCA ends to a spare audio out on your amplifier. (I used "VCR 2", but you could use the tape deck output if necessary.) From here it's like falling off a bike.

Once you get familiar with Audacity's controls, start playing your favorite record. Open a new Audacity project and click the record button. Adjust the input level until the meter just barely doesn't top out. You can also look at the wave form, the loudest portions should be not quite as tall as possible. Once everything is set, close the track you've been recording, and start a new one by hitting record, play your record and sit back. When the album side ends, click stop, and save the project.

You'll probably want to clean up the recording. I've found that using the "noise removal" and "click removal" to be pretty effective. For the noise removal, select a couple seconds of quiet between songs, or at the end of the record. Choose Effect > Noise Removal, then click "Get Noise Profile". Now select your whole recording. Again, choose Effect > Noise Removal. This time you want to click "Remove Noise". I find moving the slider two spots toward "less", i.e. the 5th of the 15 positions, to remove most of the noise without affecting the quality of the recording too much.

Next, while the whole recording is still selected, choose Effect > Click Removal. I just use the default. Together with the noise removal, this cleans things up very nicely. If your record has a real scratch, this probably won't get rid of it completely, but if your record is in good shape, you can get a very nice recording.

Now for the tedious part. Select each song separately, and choose File > Export Selection as MP3. Fill in all the information in the dialog boxes and save the file somewhere that you can find it easily. Once you've done that, drag all the mp3 files onto the iTunes icon, or do whatever else you do with your mp3's. You're good to go.

Audacity does a great job, but it is free, and there are a few bugs. For instance, if your screen goes to sleep while you record, there is a slight skip in the recording. If all your recording have a skip at about the 1 minute mark, this might be the reason. All in all, though, this seems to be pretty effective.

Thursday, August 14, 2008

Bike Log

Yesterday evening, I did a 13 mile ride at Hartwood Acres. I went out with one of the PORC groups. It was a great night. We haven't had much rain lately, so pretty much everything was dry. It was nice an cool, too, which is surprising for the middle of August.