Announcements Page

Welcome!

Hi all,

Welcome to Algorithms and Data! Our main unit page is hosted on GitHub Pages here. The first video gives a much more detailed introduction, but in short, this unit will cover material on a rolling basis. For example, for Week 1, I released video lectures yesterday evening, we’ll have an in-person Q&A on Friday, there’s a Blackboard quiz on the material with a deadline of noon next Monday (i.e. September 23rd), then we’ll have a 90-minute in-person problem class on it the same day. At the same time on the 23rd, week 2 will have its own material release, quiz, and Q&A to match a problem class in Week 3, and so on.

These weekly quizzes do count towards your unit mark, and are essentially free marks - don’t let them slip by! Again, the first quiz deadline is noon on Monday September 23rd.

I hope you all enjoy the unit - see you on Friday for the first Q&A!

Best wishes,

John

Cat of the day: Here!

Weekly Drop-Ins

Hi All,

As part of the unit we will be running 3 TA led drop-in sessions per week. These will run similarly to drop-ins from other units, and are a chance for you to bring any work or questions you’d like to discuss.

The timings of these are as follows:

Tuesday 13:00
Wednesday 12:00
Thursday 13:00

The locations haven’t been confirmed yet, so for week 2 they will run online in the dedicated teams channel. The locations will be updated once they have been confirmed.

Adi

Re/Play recording issue

Hi all,

It looks like there was a recording issue with the first problem class - it captured the monitor rather than the whiteboard, so the recording is only of the audio. Thankfully I hedged my bets in terms of what would be captured and did the second class on the doc cam, which was captured fine! The two classes covered the same material, so even if you attended the first class you should probably still watch use the recording of the second class for reference, and in future I’ll run classes with the doc cam.

(I know there can be issues seeing the doc cam at the back - if you’re having trouble seeing please don’t even put your hand up, just shout and ask me to zoom in/write bigger and I will!)

Best wishes,

John

Cat of the day: Here!

New versions of videos 3-1 and 3-4

Hi all,

Sorry about this - it looks like I failed to link two newly-corrected videos correctly this week, with the result that some errors slipped through with no visible errata on the unit page. I discussed this in the Q&A today, but the short version is:

The definition for weak connectedness stated in the 3-1 video is subtly wrong. A directed graph is weakly connected when for all vertices u and v, there is a path from u to v ignoring edge directions, not when there is a path from u to v or from v to u (but maybe not both). For example, the graph with vertex set {1,2,3} and edge set {(1,2), (3,2)} is weakly connected under the first (correct) definition, but not under the second (incorrect) definition.
At the end of slide 6, the definition of a leaf as a degree-1 vertex is correct for unrooted trees. For rooted trees, the definition is the same except that the root cannot be a leaf, even if it has degree 1.

The new videos are on the unit page now. The timestamps of the corrected sections are roughly 7:35-13:16 for video 3-1 and 13:12-16:16 for video 3-4.

Best wishes,

John

Cat of the day: Here!

Quiz 4 error

Hi all,

In question 6 of this week’s quiz (the one due on Monday), vertices are displayed in the wrong order - they are listed in the order v1, v2, v3, v5, v4, v6, … rather than v1, v2, v3, v4, v5, v6, … . You should answer the question as it is written, so put the correct position for v5 next to v5 and the correct position for v4 next to v4. If you have already answered the question and (quite reasonably) didn’t notice the order difference, then don’t worry, I will go through when all the marks are in and give full or partial credit where necessary. For example, students who read v5 as v4 and vice versa and had that as their only error will get full marks for the question. (I’ll only actually change the marks where it makes a difference, so I won’t check the quiz for anyone who got 50% or more since they’re getting the full 100% credit either way.)

With any other VLE in the world I wouldn’t be sending this announcement - since most people prefer to do the quiz over the weekend, I would simply change the display order in the question and re-mark the submissions people already made, thus solving the problem. But Blackboard says I can’t change the way the question appears on screen because people have already attempted it. Apparently to people who work at Blackboard, the thing I just said sounds in some way reasonable for ordering-based questions and only for ordering-based questions, as retroactive changes to other questions are perfectly fine.

As it happens, the moment Blackboard threw the error I let out a primal scream of rage, remembering the moment exactly the same thing happened on exactly the same question last year with exactly the same result, leading us directly to where we stand today. Due to the ravages of age, I cannot rule out the same thing having happened two years ago as well. Let’s all take this as our monthly - nay, weekly - reminder that if you end up working as an academic and your institution is considering the use of Blackboard or Blackboard Ultra as a VLE, then it is your moral obligation to use all means short of actual physical violence to prevent this from happening.

Thank you to the student who brought this to my attention - while I am quite angry right now, absolutely none of this anger is directed at you!

Best wishes,

John

Cat of the day: Here.

Clarification RE week 6 and quiz 5 deadline

Hi all,

After a question in the problem class today I realised my dates were all wrong on the unit page, and in particular that next week is reading week! As such there are no classes or Q&As next week, and the deadline for this week’s quiz is not next Monday (the 21st) but the Monday after (the 28th). The dates are fixed now, sorry about that.

Best wishes,

John

Cat of the day: Here! (Courtesy of my parents, some searching required…)