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diff --git a/docs/ta/img/vg151_e1/graph_color.png b/docs/ta/img/vg151_e1/graph_color.png Binary files differnew file mode 100644 index 0000000..6d7541e --- /dev/null +++ b/docs/ta/img/vg151_e1/graph_color.png diff --git a/docs/ta/img/vg151_e1/graph_hsl.png b/docs/ta/img/vg151_e1/graph_hsl.png Binary files differnew file mode 100644 index 0000000..97f351e --- /dev/null +++ b/docs/ta/img/vg151_e1/graph_hsl.png diff --git a/docs/ta/img/vg151_e1/graph_hsv.png b/docs/ta/img/vg151_e1/graph_hsv.png Binary files differnew file mode 100644 index 0000000..93d5c69 --- /dev/null +++ b/docs/ta/img/vg151_e1/graph_hsv.png diff --git a/docs/ta/img/vg151_e1/graph_printed.png b/docs/ta/img/vg151_e1/graph_printed.png Binary files differnew file mode 100644 index 0000000..773d2b7 --- /dev/null +++ b/docs/ta/img/vg151_e1/graph_printed.png diff --git a/docs/ta/img/vg151_e1/sierpinski.png b/docs/ta/img/vg151_e1/sierpinski.png Binary files differnew file mode 100644 index 0000000..fba2f5d --- /dev/null +++ b/docs/ta/img/vg151_e1/sierpinski.png diff --git a/docs/ta/vg151_e1.md b/docs/ta/vg151_e1.md new file mode 100644 index 0000000..18fce73 --- /dev/null +++ b/docs/ta/vg151_e1.md @@ -0,0 +1,455 @@ +# VG151 — Midterm 1: A Chronicle + +(All timezones are UTC+8) + +## 2022-10-19 10:00, Zoom + +The ENGR151 teaching team (TT for short) gathered online for our first +exam preparation. At first we thought the exam would be online and spent +an hour thinking of ways to prevent cheating, as there has never been an +online coding exam. We have a few questions on their project (for example +how did you plot your rectangles in matlab) that would be super easy to +cheat on, so Manuel proposed an oral exam (as was tried on international +students who attended this course online constantly). + +Fortunately, this exam model was never tried because we got news that next +week will be offline again, after more than one month of lockdown. + +The exam consists of two parts: part A is on paper, and part B is coding. +We created a Gitea issue to track our ideas for part B. + +## 2022-10-19 11:08, Gitea + +One TA submitted their idea to the thread. It's about [Sierpiński +triangles](https://en.wikipedia.org/wiki/Sierpi%C5%84ski_triangle). I know +where they found it: [the Wikipedia article on recursion, section "In +Mathematics"](https://en.wikipedia.org/wiki/Recursion#In_mathematics). + + + +## 2022-10-19 16:46, Gitea + +Another idea emerged. It was about a basic line interpreter that takes +a file of definitions of shapes (position, size, color, etc) and plots +them accordingly. + +## 2022-10-19 17:47, Gitea + +And here's my idea: I was taking discrete math, and in set theory they +have this trick where you represent a natural number `n + 1` with `n +U {n}` (where `U` stands for union). So, if we take 0 to be the empty set +`{}`, 1 is `{} U {{}} = {{}}`, 2 is `{{}} U {{{}}} = {{}, {{}}}`, etc etc. +Here's my code: + +``` +function set_theory + n = input('Input a natural number: '); + disp(n2s(n)); +end + +function s = n2s(n) + % convert natural number to set theory representation + if n == 0 + s = '{}'; + return + elseif n == 1 + % handle edge case where we need no comma + s = '{{}}'; + return + end + + s1 = n2s(n - 1); + % pretty much a hack: strip the trailing }, + % push s1, and put the } back + s = [s1(1:end-1) ', ' s1, '}']; + return +end +``` + +I thought it was a simple exercise, almost _too_ simple as long as you +know how recursion works. + +## 2022-10-20 13:06, Gitea + +Manuel has read all our ideas, and decided to go with two: + +- The shape interpreter, and +- My set theory recusive algorithm + +However, he commented that the interpreter needs to be more challenging, +and that he will remove the set theory notation from mine in favor of +something else, but it remained a mystery at the moment. + +## 2022-10-20 17:15, Gitea + +Babe wake up, new interpreter specifications just dropped + +We added: + +- `compose` instruction that works like classes +- fill colors +- absolute or relative movement + +## 2022-10-21 21:15, Mattermost + +Manuel put together an early draft of the testpaper for us to check. There +are three exercises: + +- One exercise about the shape interpreter +- One exercise about some alien sci-fi in the Minami-ke lore +- One exercise about RGB image manipulation + +The sci-fi goes like this: (paraphrased) + +Minami Haruka shows her sisters a weird device she found with a keypad and +a screen. When she presses 0, screen reads `-.`; 1 → `--..`, +2 → `--._--...`, and 3 → `--._--.._--._--....`. + +Kana suspects that aliens are using this device to "communicate as they +plan to invade campus", but Haruka found a pattern. What pattern? + +`-` is `{`, `.` is `}`, and `_` is `,`. + +Now that the lore is over, the questions are + +- What is 4 +- Diagram of recursion +- Base case +- Steps repeated +- Describe algorithm +- Implement algorithm +- What is 12 + +I admire Manuel's imagination that exploded an innocent set theory +notation to make such a bizzare scenario. + +Also, another side effect is, the order of this sequence is well-defined. +No need to worry about `{{}, {{}}}` and `{{{}}, {}}`. + +## 2022-10-22 19:28, Mattermost + +Manuel sent us his semi-ready version of the testpaper, on which +I discovered a flaw: + +> Convert from hexadecimal into binary: 16, AG. + +I reported it to Manuel, expecting him to fix it: + +> pretty sure `AG` isn't a hex number + +Here's how he replied: + +> `AG` i know this is not hexadecimal, but do they? :smirk\_cat: + +> I like tricky questions... + +> when they ask us duirng [sic] the exam we just tell them if they think +> there is a mistake they explain it + +At this moment I knew our students are about to be bamboozled. We'll wait +and see… + +Also, there was a sample output image for the shape interpreter exercise. +On the screen it looks like this (cropped so I don't get sued): + + + +However, I'd imagine the paper would be printed in grayscale, which means +it will look like this: + + + +Manuel changed the grayscale method to HSL (Hue, Saturation, Luminance) so +it looks better: + + + +## 2022-10-23 11:00, Mattermost + +A few more typos and ambiguities are fixed, but there came another +problem: the image Manuel asked students to manipulate, `forest.tif`, is +part of an image processing toolbox, so we switched to `corn.tif` to be +safe. + +## 2022-10-23 17:19, Mattermost + +The exam papers are ready for printing. + +## 2022-10-26 13:18, Gitea + +I created e1 repos for everyone and drafted an announcement for testtakers +to clone it. + +## 2022-10-27 13:50, UEO + +Menako got the exam papers in a bag from UEO. + +## 2022-10-27 15:45, exam room + +We had 85 students — 78 of which took the exam offline. We had 44 in our +exam room, the rest in another. + +We unsealed the package of testpapers, and found this thing: + + + +As a fix, when part B began we would project the image we intended on the +screen. + +## 2022-10-27 16:00, exam room + +The bell struck and the exam commenced. Little did they know, they were in +for a big surprise. Hands in the room I proctored rose in confusion. +"Excuse me," one asked, "this question doesn't look quite right to me." + +I asked, "what's the problem with it?" + +They replied, "I don't think `G` is a—" + +"Just write down what you think. Manuel's probably thinking the same +thing." + +Participatory exam: an exam where students are not the only ones taking +it; instead, proctors play a major part in maintaining the effect of trick +questions. We indeed tried very hard not to spoil it. + +It's official folks, exam proctoring is a performance art now. + +## 2022-10-27 16:30, exam room + +Time for part B. I walked around, and was amazed by the multitude of +laptop models in the modern age. I guess half-tablet half-keyboard C-sides +are a thing now? + +At least three testtakers got confused halfway through exercise 3, waved +at me and asked "what's the corn image?" I shrugged and told them to read +on. + +## 2022-10-27 17:35, exam room + +One testtaker raised a question: + +In exercise 1 (shape interpreter) we provided some sample code to be +interpreted. One line goes + +``` +square background cyan (0,0) 20 20 +``` + +Another goes + +``` +square road black (0,-5) 10 +``` + +Obviously they are off by one parameter. Turns out the specification and +the second line were changed, but the first one wasn't. We ended up +issuing an erratum 10 minutes before the exam ends. + +## 2022-10-27 17:45, exam room + +It's time to submit everything to Gitea. I had a flash drive in case +someone's antenna melts, but it turned out unnecessary. The process was +simple as `git add ./; git commit -m 'e1'; git push` then opening +a release called `e1` on Gitea. + +We collected and counted the exam papers, then dismissed the exam. + +## 2022-10-27 17:57, exam room + +All e1 repos are archived. As our room was mostly empty, we went ahead to +the other room which Manuel was a proctor of. + +I assigned myself to exercise 2 of part B, because that's the way karma +works; I contributed the idea after all. So did the TA who made exercise 1. +Menako assigned herself to most of Part A, and expected to begin grading +that night. + +Discussion rooms in Longbin Building, the official building of Joint +Institute, were not open for booking, so we had to use Manuel's office. He +handed Menako his key. It was the rarest of in-game items, uncraftable by +any means. + +## 2022-10-27 18:37, McDonald's + +The rest of the TA group had plans that night so Menako and I had burgers +at McD's, then rode off to Longbin Bldg. + +## 2022-10-27 19:00 or something, Manuel's office + +Manuel's office is tiny. Crappy monitor, crappy keyboard, but many chairs +and a bookshelf of math textbooks. + +Exercise 2 was the only one in part B to require answers on paper or the +README file, so the first thing I did was to classify the answer sheets +based on where they wrote them. That night I graded everything on paper, +but wasn't able to read all the README files. + +Menako, on the other hand, graded part A with blazing efficiency. What +quickly grabbed our attention was how she should grade the `AG` question. +After some discussion, we agreed upon this rubric: + +- If you think `G` is 16 (or any other number), you get zero points. +- If you leave this question blank, you get full marks. +- If you explain that `G` is not a hexadecimal digit, you get full marks + plus a star (no points, but it's a token of prestige). + +She finished her part that night. + +## 2022-10-27 23:00 or something, [undisclosed location] + +I need to come up with a way to grade the last question (what is 12) +without going through the trouble to scan through all 10,239 characters +(that's how long it is). And the solution? Checksum. + +I grep'd everyone's README.md for >10k-character long sequences of `-_.`, +piped them to md5sum, then sorted them. The command is + +``` +$ grep -hoE '[-_\.]{10000,}' FILE.md | md5sum +``` + +There were 7 different versions: + +- One is empty; +- One is correct; +- One is correct if you strip one dot (they wrote it in a markdown ordered + list) from the beginning; +- One is truncated at 10k characters because they copied it from the + variable window instead of command window. No point for you, sorry. +- The other three are incorrect. + +Subsequently I spent a dozen minutes committing the grades with a red pen +on paper. As this question is worth one point, I just treated it as +atomic. + +That night I also graded all the README's. + +## 2022-10-28 12:55, Manuel's office + +The next day I went back to Manuel's office again, this time to get things +done for once and for all. All my colleagues came along (except Menako). +The desk was crowded but fortunately I'm mostly done with paper, so I took +a corner to grade all the code. + +My rubrics are based on four criteria: + +- Base case (2pt) +- Recursive case (3pt) +- Coding style (1pt) +- Your code doesn't crash (1pt) + +Yes, if your code is unindented or looks like a mess, I will take away one +point. + +And there are two special rules: + +- Iterative algorithms get no point +- Marginally recursive algorithms get 4pt max. + +What counts as marginally recursive? Well, consider this Python snippet: + +``` +def alien(number, string, target): + if number == target: + return string + string = string[:-1] + "_" + string + "." + return alien(number + 1, string, target) + +print(alien(1, "--..", 3)) +``` + +Does it work? Yes. Does it yield the correct result? Yes! Is it recursive? + +…Maybe? + +I mean, it *does* call itself. But it's not what we meant! Observe how +`number` grows larger and `string` longer as we go to the deeper level. +Recursion as we taught in the lectures was the opposite: breaking down the +problem until it falls within the base case(s). Furthermore, this is tail +recursion, which is just iteration with extra steps. + + +## 2022-10-28 16:42, Manuel's office + +Part A is finished for all paper submissions. + +## 2022-10-28 17:09, Manuel's office + +Part A is finished for international students also. + +## 2022-10-28 20:21, Manuel's office + +Grading finished for the whole exam. + +## 2022-10-28 20:34, Mattermost + +We begin discussing curves. Manuel remarked: + +> no rush to publish grade. you graded too fast!! + +and + +> fastest 101/151 grading ever!!! :partying_face: + +We decide to delay the release, at least not until the next weekday. + +## 2022-10-29 10:02, Mattermost + +Remember on 2022-10-23 we switched to `corn.tif` for Part B ex3 "to be +safe"? Huge mistake. It turned out, `corn.tif` wasn't an RGB image as we +thought it was — it was an _indexed_ image, which means it comes in two +parts: + +- A list of key-value pairs of color indexes and RGB values +- A matrix of indexes + +To convert it to RGB, you need to call `ind2rgb`. At first this was part +of our rubric, but after a while we found it too harsh, so we just awarded +points to whoever processed it correctly as if it were RGB. + +## 2022-11-01 09:00, Canvas + +Grades are released. Paper checking is scheduled at 2022-11-03 +20:20-22:20. + +## 2022-11-03 20:00, meeting room + +I arrived at the meeting room reserved for the paper checking session and +laid out the testpapers. A few eager students were waiting outside. + +As time went on, the room became increasingly crowded. A line appeared by +my side, asking for points. + +The single most asked question is: + +> Why did I get zero for "write an algorithm"? I wrote it in my code! + +For context, we have two contiguous subquestions: + +- Write an algorithm describing how the conversion works +- Implement the algorithm in matlab + +Both were assigned 7 points, so you see the importance of the former. What +I was expecting was: + +- A piece of text +- Pseudocode +- Comments in code + +Sadly, many assumed "my code is self-documenting, it answers both +questions." Sorry, you're misinterpreting what we meant by an algorithm. + +There was one case though, I forgot to check someone's README file +somehow, and wasn't aware they wrote pseudocode. I read it, and it made +all the sense I wanted to see. Ka-ching, 7 points. The same person had +their Part B ex1 grade bumped by 6 points (grade looked like 10, but was +actually 16). That's 13 points in total. _So lucky._ + +## That's a wrap! + +This is everything that (a) I feel like sharing and (b) I am allowed to +share. |
