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All entries for Thursday 02 June 2011

## June 02, 2011

### Linear Algebra MA106 Exam Reflection

This year’s exam was written by a different person (Daan Krammer) to the previous years’ and so naturally it differed. In particular, the last question wasn’t a series of true/false, which I preferred for easy marks and occasional interesting point (and nice tricks – an identity map is not always an identity matrix, for one).

As before, I did past paper questions, got bored quickly, and flipped through the markschemes the morning of the exam. I did find a much better (shorter) “ranks are equivalent” proof than the one I’d previously learnt, so it wasn’t a complete waste of time.

The first question was standard fare even for previous papers. One question was awkwardly phrased, so I decided to take it literally. The second dealt with surjectivity and injectivity – a new topic for exams, but one I’m pretty sure was dealt with in assignments. The third contained a matrix proof where I couldn’t be bothered to memorise the subscripts involved, in the hope it wouldn’t come up – ah well. The fourth contained a horrible “find this 5×5 matrix determinant” that I got terribly wrong. The last part of four was an interesting original proof in which I used parts of my old rank-equivalent proof, mostly relating to bases of row spaces and the like. The fifth, which I didn’t do, was full of questions that would be easy to work backwards. I was turned off by the hint to the second part, which I couldn’t comprehend in the time limit.

Overall I think I did pretty well, but I may have got large swathes of it incorrect. Nonetheless, it was a more interesting exam than the previous ones – original proof questions are very fun if you get them.

### Probability A/B – ST111/2 Exam Reflection

Probability was the first Maths exam I took this term, on the 31st. I had a bunch of past papers, but the lecture notes were still incomplete. No answers were provided for any assignment bar the last, but I got most of the marked questions right, and probably most of the rest of the questions as well.

I did…around 3 past papers of the old style, and one or two newer ones. I skipped some of the questions of PGFs and the like that aren’t in the syllabus. Before the exam, I felt like I’d done enough revision – more that I didn’t feel like doing any more.

The exam itself was split into two parts: A and B. A bore some resemblance to past papers but had a fair few questions on the theory, the like of which hadn’t come up before. I was glad I picked Games & Decisions at this point, as the extra work on basic probability helped.

I think I did pretty well on Prob A, overall. I was able to answer all of the questions, which is a good sign. I wasn’t exactly sure what “basic set operations” were, though, especially when Probabilities are added to the mix.

Probability B was different. I couldn’t remember how to find joint or marginal densities, the version of Markov’s inequality was different to the one I knew, and I thought that a question asking for an expected number of offers relating to “a” (nonspecific) cdf F meant to average over all possible cdfs, so one question was right out. 4 past paper sub-questions came up, so that was very convenient. Couldn’t remember exactly how to find P(X < Y) given distributions, did a double integral that seemed reasonable at the time.

Overall, I think this exam went very well, although as it was the first I did more revision on it than I have for many other subjects (there were more past papers available, too). I think I did *too much* revision – I could quite easily have done substantially less and got a similar mark. I am planning on doing more Stats later, though, so no harm.

### Post #1

And so I decide, at the end of the year, to get a blog here. A blog seems rather an awkward callback to the halcyon days of livejournal or such. I suppose these things were rather more popular approximately five years ago.

I was pretty late on the social scene in the first place – I am an incredibly introverted person – I got a Facebook account last year, I believe.

The general aim of this is to make some random posts on whatever strikes my fancy. I’d also like to use it to reflect on how exams went – which is the main point I’ve set it up now, in all honesty.

But for now, miscellany:

I thought I knew pi to 30 digits (why did I memorise them? I wanted to, I guess); but while attempting to speak the digits of pi in Japanese, I discovered that I actually only knew it to 4. I knew how to say the 30 digits in English, but just thinking of the numbers directly – I couldn’t connect them. I realised this on the first go, but did much better on the second and third try by means of just remembering what I’d done before – still, the first time was a surprise.

Costcutters’ is currently having a sale on chocolate fingers, so I indulge in my terrible vice. I feel they’re far too expensive at £1.79 each, but upon cutting down to £1 I suddenly feel the urge to stock up. I can finish off a pack a day, and sometimes more. Pringles, too.

The current Mathstuff logo is the first time I’ve seen GIF compression in a loong while.