Now that I am teaching Math 285 (shorter version of 286) I am using my differential equations notes again. Furthermore, a friend of mine is using them for a reading course for a student. Hence lots of typos and errors are being found. On the errata page I only list the serious errata, not simple grammar problems and such. For chapters 0 and 1 (the ones I covered so far), I have had 14 errata. That’s about 2.7 pages per one erratum. That’s not too bad I suppose. Especially given that there was no editorial process yet. I suppose one can expect a similar rate of errors later on, though some of the later chapters have had a lot more work put into them, so I hope they are more correct. For example, the PDE chapter and the eigenvalue chapter had large parts used twice already, so I assume I have caught more bugs there.
Anyway, I went through certain parts of the notes today and found 5 errata (chapters 2 and 6). My most common mistake (actual mistake that was not caused by a simple typo) is forgetting to apply chain rule somewhere. By reading ahead, I am trying to cheat my students out of extra credit (they get points for finding new mistakes in the notes)
Today they had a test and I noticed a rare phenomenon. A 3-chain of students trying to copy (I don’t believe they were very successful). One was trying to copy from another who was trying to copy from another. The last person in the chain was not even being very careful about it, but I suppose that if any information passed through the chain, then it ought to be garbled beyond recognition by the time it reached the end. I am sure that this is a very noisy channel.