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Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

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Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#41
post #6

I wish I came across the so called proof-based math before calculus and trigonometry. It would have grabbed me instantly. High school math (and especially physics) classes would leave me with very uneasy feeling that something crucial is left unmentioned, something important is swept under the rug and something important is hidden for whatever reason. Turns out I was wanting for proofs, but couldn't articulate it - I…

Brewster Kahle (of Alexa and Internet Archive fame) went this way: he and his wife decided that school wasn't right for their younger son so the two of them (father and son) worked through Euclid together.

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#42

Earlier quoted context omitted.

Your high school didn't teach geometry?

My kids are in high school right now. I was getting my daughter psyched up for geometry, by promising her that she'd get to do proofs. The geometry class completely glossed over proofs. It was much more oriented towards solving problems. I don't know if it was because of standardized testing, but I have my suspicions. Fortunately, my daughter worked on the proofs herself, outside of class. I was saddened for many rea…

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Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#43
Regarding item 10 in that list, I learned plenty of Laplace transforms, partial fraction expansions, stability, phase planes, etc. It's the core of control systems theory. It was just not taught in differential equations class. The DE class was a bag of useless tricks. All the other EE classes were very useful tricks of how not to directly solving DEs.

Going to drink a beer now for Oliver Heaviside. The invention of the Laplace transform is one of the greatest contributions to engineering.

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#44

Earlier quoted context omitted.

Funnily enough, from a mathematical point of view, it's the opposite: integration is a really nice operation that can be applied to basically anything, whereas differentiation is really finicky, sometimes derivatives don't exist and you can't even be too sure when, so you need to be extra careful. This carries over to doing numerical computing: integrating an arbitrary function is easy, for smooth 1d functions it's a…

More like `from a computational point of view.' Analytically, integration is much more difficult and richer than differentiation!

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Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#46
post #20

It's sad one needs to reinforce the teaching of concepts rather tricks. Even worse is when you have all the proof based and concept oriented course and are tested on trickeries on exams.

My high school calculus teacher was really great at this. He didn't just teach a bunch of transformations to memorize. That was part of it, naturally, as you aren't going to use the definition of limits and the FToC in all your problem solutions. He actually made us construct volumes from pieces of poster board, measure the segments and calculate the Riemann sum. When we did function analysis, he didn't allow us to use the Cartesian plane at first. We had to show visually how a function deformed the one-dimensional real line. How x^2 squished values between -1 and 1 toward 0 and stretched the other values toward +infinity.

It gave me a good "visual" grasp of the concepts and made most of my higher math classes much easier.

I do agree diff eq instruction sucks. I got an A in that class and didn't understand a thing. "This equation has this form; this is the canned solution."

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#47

Earlier quoted context omitted.

Your high school didn't teach geometry?

Geometry proofs aren't real proofs.

They certainly are. Also, geometric proofs are considered the origin of all mathematical proofs. They might seem crude, but open up to any chapter in Elements and you'll see many difficult problems solved using those 5 axioms.

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#48
post #17

Earlier quoted context omitted.

Funnily enough, from a mathematical point of view, it's the opposite: integration is a really nice operation that can be applied to basically anything, whereas differentiation is really finicky, sometimes derivatives don't exist and you can't even be too sure when, so you need to be extra careful. This carries over to doing numerical computing: integrating an arbitrary function is easy, for smooth 1d functions it's a…

Only numerically? Analytically, differentiation is much easier and integrals are tough or impossible, unless I'm missing something.

I think he means something like the difficulties shown by https://en.wikipedia.org/wiki/Weierstrass_function . There are a lot of conditions a function must satisfy to be differentiable.

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#49

Please teach calculus before teaching trigonometry. There's no prerequisite to learn trig first, and forcing people to learn trig-calc excites many mathophiles but is a major turn off to other students. Calculus can be taught using just basic algebra, and most students will benefit from already understanding calculus, when they are learning trigonometry.

Certainly integration of trigonometric functions, requiring trigonometric identities, seem to get more time allotted to them than the pedagogical value they provide AFAICS, but I'd be interested to hear someone pointing out what I'm missing there.

Re: Lessons I Wish I Had Learned Before Teaching Differential Equations (1997) [pdf]

#50
I TA'd for an undergrad ODE course for two semesters. I'm a grad student at a public university with very good undergrad engineering students. Nonetheless, with the course I taught, at least, the main problem was that WAY too much was packed into a single semester. I suspect that this is the same everywhere. For example, about a month and a half of the course was devoted to systems of linear equations. These were students who, a priori, knew basically no linear algebra, being asked to understand an entire linear algebra course, with some extra stuff thrown in (you know, the differential equations), in six weeks. In order to solve a general system of constant coefficient linear odes, you have to take a matrix and compute its Jordan canonical form. The students I taught were performing this calculation by the end of the unit, but it was of course a joke. On their exam, they were asked to do this calculation (in differential equations language), and most of them were able to do it because they were good students and had memorized the procedure. Then, in another question, they were presented a 5x5 matrix, told that its only eigenvalues were 2 and -2, and asked if it was invertable. I don't think anyone gave a reasonable answer.

What is the point of that?

Edit: Everyone should be aware of this amazing Gian-Carlo Rota quote, the entirety of a book review on contemporary philosophers: "When pygmies cast such long shadows, it must be very late in the day."

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