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

308 点作者 capocannoniere超过 7 年前

19 条评论

woopwoop超过 7 年前
I TA&#x27;d for an undergrad ODE course for two semesters. I&#x27;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&#x27;t think anyone gave a reasonable answer.<p>What is the point of that?<p>Edit: Everyone should be aware of this amazing Gian-Carlo Rota quote, the entirety of a book review on contemporary philosophers: &quot;When pygmies cast such long shadows, it must be very late in the day.&quot;
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stephengillie超过 7 年前
Please teach calculus before teaching trigonometry. There&#x27;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.
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fmap超过 7 年前
And 20 years later, this essay is still as relevant as the day it was written. I agree with pretty much everything that&#x27;s in the essay, except for a few small points.<p>&gt; There is nothing wrong with keeping the functional notation for density functions – as physicists and engineers always did – as long as one bears in mind that density functions cannot be evaluated, but only integrated.<p>This always bothered me, since, as noted in the very next section, distributions don&#x27;t have an analogue to pointwise multiplication. Even worse, there is a perfectly servicable notation for such &quot;dual functions&#x2F;vectors&quot; that physicists have been using throughout the second half of the 20th century. We could just use a consistent notation and not confuse new students, but no. &quot;It&#x27;s always been done this way&quot; is a terrible argument and leads us to the confusing mess of notations that people still use for integrals and integral transforms...<p>---<p>Apart from that I would teach people recurrence equations&#x2F;stream calculus before going into the limiting case of differential equations. It&#x27;s true that differential equations are sometimes easier to handle analytically, but this is neither relevant (as the article notes) nor a great point in their favor, since we just end up teaching students a bag of tricks instead of explaining why something works...
jessaustin超过 7 年前
<i>Why is it that no one has undertaken the task of cleaning the Augean stables of elementary differential equations? I will hazard an answer: for the same reason why we see so little change anywhere today, whether in society, in politics, or in science. Vested interests dominate every nook and cranny of our society, even the society of mathematicians.</i><p>Truly we live in a decadent age. With this much fuel piled up, who will be surprised by the conflagration?
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inbox超过 7 年前
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&#x27;t articulate it - I just sensed that something was off :)
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madengr超过 7 年前
Regarding item 10 in that list, I learned plenty of Laplace transforms, partial fraction expansions, stability, phase planes, etc. It&#x27;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.<p>Going to drink a beer now for Oliver Heaviside. The invention of the Laplace transform is one of the greatest contributions to engineering.
mathattack超过 7 年前
Apparently he passed 2 years after this was written. RIP. A great mind.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gian-Carlo_Rota" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Gian-Carlo_Rota</a>
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tempw超过 7 年前
It&#x27;s sad one needs to reinforce the teaching of concepts rather tricks.<p>Even worse is when you have all the proof based and concept oriented course and are tested on trickeries on exams.
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hprotagonist超过 7 年前
you can fake knowledge of undergraduate differential equations if you know about 3 hours worth of linear algebra.<p>More profound understanding is difficult but not terribly impossible.<p>The best diffeq text i&#x27;ve found is by Blanchard, DeVaney and Hall, and it remains the only math textbook i&#x27;ve ever been able to read.
abhirag超过 7 年前
I have realized that Difference Equations i.e. the discrete variant of Differential Equations are much more common in Computer Science&#x2F;Data Science(recurrence relations etc.) and it would have been great if they were atleast given half as much attention as Differential Equations get in universities.
falcor84超过 7 年前
I&#x27;m not sure how well it would fit as a first course, but the thing that really helped me understand what&#x27;s behind differential equations is Steven Strogatz&#x27;s wonderful book &quot;Nonlinear Dynamics And Chaos&quot;[0].<p>[0] <a href="https:&#x2F;&#x2F;www.amazon.com&#x2F;gp&#x2F;aw&#x2F;d&#x2F;0813349109&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.amazon.com&#x2F;gp&#x2F;aw&#x2F;d&#x2F;0813349109&#x2F;</a>
burnerOh2125超过 7 年前
Interesting, I&#x27;m a phd-drop out in computational biology, working as a data science consultant: I use mathematics including multi-dimensional statistics, linear algebra, and calculus everyday. Being self-taught, I&#x27;m very self conscience about the math I don&#x27;t know, but so far, not knowing differential equations doesn&#x27;t seem to have hurt me. I actually just ran into a problem that uses Hamiltonian dynamics, so maybe I will end up learning differential equations, but it does seem like the course, as taught many places and in the Dover books I own, presents either no useful conceptual insight, like why I learned geometric algebra, or a powerful toolset, like some multi-dimensional statistics.
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ben_jones超过 7 年前
My differential equations class was the only course I ever took with over 30% of the final grade being derived from homework assignments. Unsubstantiated - but my peers and I all believed this was because everyone was failing and dropping the course.
gumby超过 7 年前
Due to an offhand comment from a friend, I started my kid on continuous math, not discrete like they do in school. Went great, until about grade 4 when they actually started to care whether he was aligned with his classmates. Germans are actually pretty intolerant of non-professional pedagogues teaching kids.<p>But it greatly improved his grasp of elementary math as it matched what he saw in the real world.
colinator超过 7 年前
<i>My colleague’s error consisted of believing that the more testable the material, the more teachable it is. A wider spread of performance in the problem sets and in the quizzes makes the assignment of grades “more objective.” The course is turned into a game of skill, where manipulative ability outweighs understanding.</i><p>Sounds familiar.
Chris2048超过 7 年前
Previous Discussion: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11207183" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11207183</a>
katastic超过 7 年前
I took two courses in ODE. I got an A in the first semester. I still have no idea what they are or what&#x27;s going on. It&#x27;s all just relationships and patterns to me--but with no intuition or understanding behind them. It never &quot;sunk&quot; in like Calculus did where &quot;Area under the curve&quot; and &quot;tangent line&quot; are super obvious in retrospect and immediately applicable to your daily life. &quot;What&#x27;s velocity? The change in distance over a unit of time.&quot; Done. Presto.
johan_larson超过 7 年前
When engineers and scientists have to get some real work done with DEs, what do they do? Is it all solved numerically these days?
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eli_gottlieb超过 7 年前
&gt;A teacher of undergraduate courses belongs in a class with P.R. men, with entertainers, with propagandists, with preachers, with magicians, with gurus.<p>Well <i>that&#x27;s</i> depressing. If not undergraduate courses, where do people expect graduate students to come from?