Pytables/Numpy: lesson learned

Today's PyTables/NumPy lesson that I learned the hard way (i.e. through time wasted): When you use the __getitem__ method from a PyTables Table, and you pass an integer, you don't get back a record array. You get back the same thing as if you pass an integer to the __getitem__ method of a record array - namely a numpy.void instance, which is used presumably because NumPy doesn't know what to call whatever you have stashed together in one record.

Multiplying lots of matrices in NumPy

The other day I found myself needing to perform matrix multiplication in Python, using NumPy. Well, what's the big deal, you say? You do know that there exists a dot method, right?

Yes, I do know that, you smart internet person you. However, my problem was that I had a number of matrices for which I wanted to perform the same type of matrix multiplication. I had on the order of a hundred thousand five by two matrices that were to be transposed and multiplied with another hundred thousand five by two matrices.

Well, duh, you say. The dot method can handle more than two dimensions, you know. Yeah, I know that as well. However, it doesn't handle it the way I needed for this task. I wanted to end up with a hundred thousand two by two matrices. Had I used dot, I would have ended up with a hundred thousand by two by hundred thousand by two matrix.

So, I had to improvise:
>>> A.shape
(100000, 2, 5)
>>> B.shape
(100000, 2, 5)
>>> result = np.sum(np.swapaxes(A, 1, 2)[:, np.newaxis, :, :] * B[:, :, :, np.newaxis], 2)

Kind of involved, but it worked. I got the initial idea from here, but the solution given here only works for symmetrical matrices - for non-symmetrical ones you have to shift the newaxis one step to the left, or it will violate the broadcasting rules of NumPy.

Super Size Suckage

Well, here's an uncontroversial post. I saw Super Size Me the other day. And I thought it sucked.

I'm not the first to do so, but that's what I have to say today. So I might as well detail my criticism a bit more, to make it more constructive.

The premise itself is kind of funny, and the main reason I watched it was to see how much weight this guy could gain in a month. Little did I know that this was to be the subject matter of only thirty percent of the movie, whereas the rest... sucked.

My experience based on previous such documentaries (Michael Moore, i'm looking at you) is that when the documentary maker has a very specific axe to grind, you just end up disbelieving everything that is presented, and you're actually trying to find flaws with the presentation. This is what I ended up doing. And the reason was that I very quickly got a lasting impression of the documentary film maker, which can be summed up thusly: "My vegan girlfriend hates McDonalds and I want to make a documentary. Why not kill two birds with one stone?" Seriously, that girlfriend should have been left out of the movie. I cringed everytime she said anything, because it was always about how superior organic and vegan food was. In the end, when she said she would 'cleanse' Morgan's post-experiment system with her special vegan diet, I cringed doubly.

Now, the above was mostly a gut reaction, but it is symptomatic of one of the biggest problems with this movie: It's not clear what in the world it's trying to say.

On the one hand, it seems to say that McDonalds is bad, and that's the take-home message. On the other hand, it seems to say that organic? vegan? food is the best. And then on the third hand, one premise of the movie seems to be that a guy is trying to eat as much fast food as he can for a month and see how that affects his health and well-being.

Then you might say, 'Well, all of these are tied together and they make up one coherent story'. But they don't. First of all, McDonalds being bad is not the same as vegan and organic food being the best. In fact, I think you will find a lot of people who would agree with the former (to some extent) but not to the latter statement. Second of all, you don't prove that McDonalds is bad by EATING TWICE AS MANY CALORIES PER DAY AS RECOMMENDED. That just proves you're bad at cause and effect.

A much better demonstration that eating McDonalds is bad for you would be to eat the recommended number of calories each day, but eating only McDonalds. If he had eaten five thousand calories worth of vegan food each day he would also gain weight.

As for the 'results' of this exercise, they're pretty much worthless as scientific facts towards demonstrating how McDonalds is bad for you. Very few of the changes that happened to his body can be said to be due solely to the fact that he was eating McDonalds and not to the fact that he was eating way too much. And some of them were pretty subjective. "I feel horrible". "My arms are twitching due to all the sugar". How do you know that?? "My sex life went down". Well, when you're binging on McDonalds food and have a vegan girlfriend, what do you expect?

Also, the most interesting result - how fat he got, was pretty underwhelming. He gained around ten kilograms, and I hardly noticed him getting fatter.

Another underwhelming result was how many times he had been asked whether he wanted a super-size menu, which was something he touted in the beginning of the movie. That was presented as one of the 'dramatic post-movie facts', you know - the ones that accompany some picture of whatever illustrates the fact best at the movie's end. He ate ninety times at McDonalds during this month, and was asked about a super-size menu nine times. Out of ninety. That's ten percent. I'm underwhelmed.

In addition to these things, you had the stock-standard Michael Moore-ish strawmen interviews, tying together unrelated facts to make a point, etc. that generally simply helped discredit the maker of the movie.

In short, I wish documentaries like this didn't get so much attention. I want to be on the right side of issues like this, but when the people who are supposedly on the right side use the same dirty tricks as those we claim to be fighting against, the lines get blurred. If what is presented is truly something that we should be shocked and appalled about, the facts will speak for themselves, and we don't need some dude or his vegan girlfriend to mix them together into a milkshake of dubious factual value.

Scheduling

It's weird how certain concepts simply stay out of your field of 'conceivability', so to speak, until they suddenly pop in and you feel silly for not considering them earlier.

Setting up a schedule for myself has been such a concept. I have read about the concept and its advantages several times before, but for some reason I have just shrugged and never considered it seriously. And I don't really know why - that's the paradox of gestalt shifts - once you have shifted, you're unable to see the reasoning behind your old view (unless you have written it down, or something like that).

I believe that perhaps part of the reason I have been reluctant to set up a schedule is my slightly irregular sleeping habits. I have thought it more important to be rested than to wake up at a certain time. And I still do - working ten hours at sixty percent is worse than working eight at ninety. And my brain is really sensitive to this. It's like sleeping badly puts some kind of insulator between the synapses so they're unable to fire properly.

However, there are a couple of reasons I presently have for willing to try out a schedule nonetheless:

If it turns out that I'm unable to function properly because I am determined to wake up at a certain time, I could always wait with setting up the schedule until morning the same day. That way, I know how much time I have for disposal.

However, I presently have another theory: That my irregular sleep is in part due to my not having any obligations to get up in the morning. Currently, I have a research position, which means I can pretty much come and go as I want. Could this have a negative effect? Perhaps if I approach it more like I would a regular job, my brain somehow would get more 'incentive' to sleep properly during the night? You see, my problem isn't that I cannot fall asleep in the evening - I usually do pretty quickly. Rather, the problem is that my sleep is light and not 'restful' enough. Also, I usually wake up before time, and if I get up at that time, I will be tired.

In other words, this is going to be an experiment. I will schedule the following day the night before, including a time at which I wake up and a time at which I go to bed, and everything in between. Naturally, it will be impossible to follow such a schedule to the point - unexpected events do occur, of course, and there are some tasks which are hard to approximate in terms of time needed for completion. However, those things I believe will come with experience. The first hurdle is actually following through with it.

Game review: Phoenix Wright: Ace Attorney

Despite all my wishes to be a productive person, sometimes I somehow end up playing some computer or video game. Recently I have been playing Phoenix Wright: Ace Attorney, and thought I'd just briefly review it.

First off, I don't like assigning one number to games, since the quality of a game can have many dimensions. SO I'm just going to write what I like about the game and what I don't like.

The premise

The game I played is for Nintendo DS, and it's a kind of point-and-click mystery solving and courtroom game, which to my knowledge is pretty unique in the market. It's animated with semi-moving anime frames. You play as Phoenix Wright, a lawyer straight out of law school, as he takes on his first cases as a defense attorney. The first mission is a simple trial, where you have to pick the witnesses testimonies apart, pressing every point and using evidence to bring to light contradictions in their testimonies. Later, you also play the role of the evidence-gatherer, which you usually do much better than the local police force anyway. There are several clashes with the arch-nemesis, Miles Edgeworth (who has later gotten games of his own). This game is the first in a series of several.

The good

Phoenix Wright (the character) is pretty awesome, although playing the game I got a different impression from what I had from all the internet memes about him.

Y'know - these ones.

He's a bit more insecure than I thought prior to playing. But I like the character, and Miles is also pretty cool, although sometimes I wish the anime industry would find another archetype than the 'brooding dark-haired guy' to be the cool dude.

The trials are hilarious and very entertaining. Whenever you manage to point out a contradiction and cool music starts playing, you feel like being a defense attorney would be the coolest job in the world. There's plenty of humor there, and especially if you're geared towards Japanese-style humor, you'll laugh out loud a lot. I did, at least. Most trials are pretty far-fetched in terms of how they are conducted and what is accepted as evidence and so on, but it's not much worse than your average American lawyer show.
Also, I want to mention the 'effects' as a good point of this game. In trial, when the attorneys are making a point, they are punching their fists on the desk in a really cool way. And whenever something 'unexpected' is happening, the effects really help bring this out by changing the music, kind of shaking the screen and in general putting surprised faces on everyone.

The bad

The evidence collection becomes pretty tedious, especially when you have to move through areas in a very slow manner (i.e. you cannot necessarily move from a given area to the area you want to be in - you have to go through all the 'intermediate' areas first).

The both

The music is really great at times (i.e. during the trials) but at other times it can get a bit jarring (i.e. during evidence collection).

The graphics.. honestly, for a game such as this, realistic graphics is by no means something I want. The graphics do a good job without being extravagant.

In summary

Despite the shortcomings of the game (i.e. the evidence collection phase) I would heartily recommend playing it, simply because they have a unique experience to offer: Being an awesome defense attorney who fights injustice and tears down even the most arrogant of prosecutors. Get your OBJECTION!s on and play it!

Check for duplicates in Python

Today's trick: Check whether a Python container cont contains duplicates!

if len(cont) != len(set(cont)): raise myError

Neat!

Fugitive.vim

All of my posts presently are written in the nick of time. It could be symptomatic of either bad planning or too much to do, but I will try to keep up the current schedule for a while longer at least.

As stated in another post, one of the plugins I am using for vim is the fugitive.vim plugin, written by Tim Pope. Its description is "A Git wrapper so awesome, it should be illegal". And so far, I have to agree - it is pretty darn awesome.

My favorite feature so far is the :Gdiff mode. It has done wonders to the tidyness of my git history. Used to be, I would edit a file, spot a minor bug that was unrelated to whatever I was currently implementing, and then I had to either a)fix the bug and implement whatever, commiting everything in one large chunk, thus messing up the Git history, or b) stash the changes so far, fix the bug, commit it, then continue implementing.

Option b) isn't actually that bad in itself. It just takes a little more time. However, if you spot multiple bugs, or do several separate modifications of the file, the stashing can get a little messy.

Now, the Gdiff command opens up the file you're editing together with the current HEAD version of that file. (Or actually, that's not exactly what is opened, but I have to research more about how Git does stuff before I have more to say). It opens these two files in Diff mode (which I didn't even know about prior to this). It then allows you to choose hunks to stage for a commit, so that you don't have to commit everything in the file at once, if you don't want to. (A hunk is one continuous piece of changed 'stuff'). However, you can even break up the hunks by specifying the lines you want to 'diffput'.

In short - it's awesome. It has other neat features as well, but those will have to come at another time. I might also write a more technical piece on the Gdiff thing.

TRAPs

As a true nerd, I am currently GMing an RPG campaign.

Preparing for sessions can be a chore - I find myself wondering how to structure the stuff I'm making up, and thinking about ways to organize often take more time than actual campaign writing.

However, there is one technique that I am extremely thankful for coming across - the TRAPs method, invented by Ry at Enworld forums: ry's Threats, Rewards, Assets and Problems (TRAPs)

Not that kind.

 
It's really making my life as a GM a whole lot easier, because it's a simple algorithm for fleshing out an adventure or encounter: Everything you add should be either a Threat, Reward, Asset or Problem. If you're introducing something that's neither, it's ineffective. And before you complain about 'atmosphere' and so on - you can easily turn either of these things into stuff that provide atmosphere.

Right now, I don't have enough time to write about this more elaborately (I have to prepare for the session), but once I have tried it out a bit more, I will try to write down my experiences.

Manual labor

A couple of times lately I have helped my grandparents do some manual labor (pruning their fruit trees and trimming the hedges).

I don't do much manual labor at home myself. I live in a rented apartment, so I don't have much maintenance to speak of, and my day job mainly consists of programming, which can only be thought of as manual labor if you are a pedant and use the original definition of the word.

But in that case, this is manual labor as well.

 However, whenever I get to do some real manual labor, I think I should do more of it. It's both due to the 'getting to work your body' thing and the 'feeling like you actually did stuff' thing. Together, they give a feeling of wholesomeness.

If and when I ever get a family and/or own a house of my own, I suppose there will be more of this. Until then, I'll just have to help out my grandparents as much as I can.

Vim

I use vim for editing.

There is no overwhelmingly reasonable reason I chose vim. Several years ago, when I first started programming on a significant basis, I started reading about the editor wars, and I immediately knew I had to make a choice and stick with it. I think the article that stands out as the main reason for my choice is this one:

Pirates and ninjas: Emacs or Vi?"

Of all the articles that could have been the basis for my choice, this is probably one of the least reasonable. However, when I did read this article, I didn't know anything about what would be useful when programming. And so, connecting both editors to ninjas and pirates made it easy to make a choice (which, I think, matters not that much in the long run anyway).

Vim: for when cannons and cutlasses just won't cut it.

Ninjas simply appeals more to me than pirates do, and knowing nothing else, I chose vim. I cannot say I regret the choice, but that could easily be just because I haven't tried emacs.

(Short aside: When I read the above article, I didn't know who Richard Stallman was. However, as it turns out, if I had known, there would have been more of an incentive to choose vim.)

Both editors benefit from plugins. I haven't manually installed many - I think the only ones I currently have installed is the fugitive plugin, written by Tim Pope, and the python indent script written by Eric McSween. I will elaborate on the former in a later post.

Of course, knowing the commands available to you is also something that makes you effective, whichever editor you use. I don't know a tenth of all the stuff that vim can do in theory, but this Stack Exchange question was a lot of help to me.

There are a couple of keybindings I find very helpful. Mapping caps lock to ESC, 't to :tabnew, 's to :w and 'q to :q are some that save plenty of keystrokes in the long run.

The more you use an editor, the better you get at it and the less you gain by switching. So it's likely I will keep using vim for the unforeseeable future. And that's ok.

Dip into finance

Today I attended a lecture by a relatively well-known academic within computational finance (the reason for this is to try to figure out what to do after what I'm currently doing).

I wasn't too familiar with the terms used within finance, so I didn't follow the discussion. In this particular course (where the speaker was a guest lecturer) they seem to use Excel a lot. Probably this is just a particularity of the course level.

One thing that really stood out was that they talked a lot about master theses. Every half hour or so, the lecturer or someone else would say something like "This is probably something that a master student could have as their project." In my field, this very rarely comes up. It made me wonder how it is in other fields. Is it a sign of underabundance of researchers within finance?

After this lecture, I am less opposed to working in finance than I previously was. I asked the lecturer about future prospects based on my own history, and she said I would have very few problems entering quantitative finance in some way - I could perhaps take a couple of courses in finance first. Also, she said that she didn't find working with finance less intellectually stimulating than what she did before (she switched to finance after her Ph.D.).

I suppose what's standing in the way of a career in finance for me is the thought that it is less 'pure' or 'ideal' than what I am currently doing. After all, working with finance is not trying to figure out how the world works. But then again - working in the academic world has made me rethink the validity of stating that I am trying to figure out how the world works. At my institute, at least, it seems to be less and less true the older you get, as grant applications, teaching etc. takes over.

I am still undecided about this. I have to try to gather as much information as possible about the experience of working with something else than what I am currently doing before I make a choice.

NumPy structured arrays

I'm programming quite a bit in Python, and my understanding of that language is incremental. Due to the nature of my work, I also work a lot with NumPy. Today I had to solve the following problem:

• Take an input dictionary
• Create a NumPy structured array with the keys as field names, the datatypes of the values as the field datatypes, and the values themselves as the array elements.

Turns out, even though i have worked with the ndarray dtype a lot, I don't have a very good grasp of the structured array. This post will not be precise, but just a summary of what I have understood today.

First of all, I thought that a structured array would be like a 'normal' NumPy array, just that one of the dimensions had field names and data types associated with them.

But I think I am wrong in this - I think it's more a matter of a structured array being a NumPy array, where each element in the array is a structure (which makes sense once I think about it).

For instance, you can't slice a structured array according to the first interpretation:

In [1]: dtype = ''.join(('uint8,', 4*'int16,', 'int16'))
In [2]: b = np.array([(0, 1, 2, 3, 4, 5)], dtype=dtype)
In [3]: b.shape
Out[3]: (1,)
In [4]: b[0, 3]
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
----> 1 b[0, 3]
IndexError: too many indices

However, if you treat the result of a slice as a separate array, it works:

In [5]: b[0][3]
Out[5]: 3

This is very basic, I know. But it's something I learned today. And that's what this blog mainly is for. Hopefully I will learn more interesting stuff later.

Bureaucracy and object-oriented programming

Today, as I had to grapple with certain aspects of real-life bureaucracy I was struck by the similarities between bureaucracy and object-oriented programming. I did a search, and found this:

Five (good) lessons the government teaches us about object-oriented programming.

I suppose there are some concepts in there that are outdated (in some communities) - for instance, I have the impression that in Python, the encapsulation concept isn't thought of as that central (cf. the 'consenting adults' paradigm). But still, the article makes good points, I think.

I think the main difference between oo programming and bureaucracy, or rather, why these concepts work so well in one case and not so well in the other, is that humans when working together as in a bureaucracy is not remotely like a logical machine. One cannot trust the output from one 'object'. The processing times are much larger. And the instantiation overhead is way too expensive in bureaucracies - people have to learn to cope with new regulations, departments, and so on.

I wonder if this can be extended somehow.. is it possible to make a model of real-life bureaucratic processing based on other programming paradigms, like a procedural programming one? If I have time at some point, I'll try to think about this more.

Wrapping your body

Sometimes I sleep badly. I have no problem going to sleep, but sometimes I wake up too early for some reason and have trouble getting back to sleep, it's as if my mind as on some kind of high (excited about the coming day, maybe?) and isn't able to calm down until a while later, at which point I have missed two hours of sleep and just know that the day is going to be crap.

As long as you are single and have flexible work-hours, this doesn't need to be that big of a deal. If you wake up early you can go do some work and then go bac k to sleep when your mind has calmed down a little. However, that's a quite limited group of people.

Something that I've experimented with the last couple of sleepless early mornings has been a relaxation technique that I did a couple of times as a teenager. It 's pretty simple - you lie on your back, calm down, and then start thinking about your toes, of relaxing them. You then move upwards through your body and focus on each body part, relaxing it, thinking that it becomes heavier. It feels a little like wrapping your body in some kind of 'Relax-o-wrap'. You end with your mouth, nose and eyes. After that, all of your body is mentally wrapped up, and you actually feel like lifting your arm, for instance, would ruin the wrap.

Then, you start focusing on your breath. You inhale deeply, down to the bottom of your lungs, so that it is your stomach that rises and falls, not your chest. I was taught to inhale through the nose and exhale through the mouth, but it's not vital. The vital part is that you focus on your breathing with your mind. In the beginning it's frustrating and hard to focus, but after a while you suddenly realize that you almost dozed off for a second. Then you actually do doze off for a second. Then for longer. Then you start dreaming - my dreams have been weird during this exercise - often they're about falling and flying etc.

After waking up, I usally do some kind of 'unwrapping' routine, focusing on each body part and making it 'unheavy' again. I don't know how important that is, bu t it maintains the illusion of a wrap around your body, which I think is important for this exercise.

So far, I haven't been able to go back to 'normal' sleep with this technique, but I find a certain type of sleep which I think is far superior to being awake. Maybe with time, regular sleep comes as well. Progress will be reported (if I can remember to do it).

Exercising

As mentioned here, I exercise regularly.

"Regularly" in this context means thrice a week, and it also means that I always exercise in the morning, right after waking up and before breakfast. Sometimes I skip exercising, though I shouldn't. Usually that's because I've slept badly (subject for another post!) and don't need more exhaustion. Sometimes it's because I was up late the day before and don't have time to exercise. Sometimes it's a combination (I slept badly, so I woke up late). But these are exceptions.

I exercise for about an hour. I usually listen to two podcasts of my favorite radio show while exercising, and they last for half an hour each.

The exercise is pretty tiring. I start with three repetitions of the following:

• x burpees (the push up + jump up variant), where x is a function of my fitness (Currently x=13).
• Shadowboxing for y seconds, where I typically adjust y so that it takes as long as the burpees do. Currently, y=45 seconds, although the burpees don't take that long, so I have to adjust a little.
• Do one more of both the above points.
• Rest for a couple of minutes.
• The Plank for z seconds, where z=90 the first repetition, z=60 the second repetition, and z=45 the third repetition.
• Rest for a minute or so.

After this, I do one more of the burpee/shadowboxing repetitions, so I do four of those altogether. Summed up, then, I currently do 13x2x4=104 burpees per exercise session. The above takes about thirty-five minutes altogether, including warming up.

After this, I do back and abdominal exercises for about twenty-five minutes, which i think is important when you sit as much during the day as I do. In between these, I do as many pull-ups as I can.

It is an important point for me to be able to exercise without too much hassle, because then I usually never get around to it. The less overhead time, the better. So I prefer to exercise at home using only body-weight. For those of us who are only reasonably fit, that's more than enough. If your goal is to stay fit, not build muscles, there really is no point in doing heavy weight-lifting, IMO. Body-weight exercise will only take you so far, though, so if you want to look really buff, then you should start lifting weights.

Or you can start doing experiments with certain drugs.

When I first started doing burpees, they totally killed me. They're one of the most exhaustive forms of exercise I know, as long as you do a proper jump up and a proper push up each time. So in the beginning, x in the above regime was about two-three. It's nice to see improvement. I am a bit unsure of doing this for a long time, though. Although it's probably better for your legs and back to do burpees than running (for a fixed amount of 'exercise'), it can still be a strain on the joints to do that many jump-ups. So far, though, so good, so I'll keep doing it until it starts hurting!

Anyway - the above regime works all major muscle groups in addition to being good cardio exercise. Combined with healthy eating, and remembering that being hungry for a little while isn't dangerous, you should notice an improvement in how you look and feel after a couple of weeks.

Interesting tasks as motivation

I used to play a lot of video games. I dread to count the hours spent doing this. Now, I don't play much anymore, though I have occasional bouts where I go on a total gaming spree. Usually that leaves me pretty depressed afterwards.

I currently have a hope that this will not happen anymore, now that I view being able to learn programming as a fun 'hobby'. That is, when I'm working on science-related stuff now, and I lack motivation, I tell myself that "once you're done with this, you can learn more programming". And it seems to work.

At least for now. I have found that many of these motivational techniques are fleeting, so it remains to be seen whether this technique stands the test of time. However, I do believe that the key to being productive is to combine several techniques that work for you. So if I combine the "learn programming once you're done" technique with some kind of variation on the Pomodoro technique mentioned in an earlier post, maybe the combination will yield good results.

In the end, though, I think it's a matter of teaching your brain to operate differently - to eke out new neuron patterns so that the brain have less resistance in those directions I want it to go. The way there can be hard and painful, though!

Presentations

Yesterday I held a presentation for a community of hobby enthusiasts in my field.

Writing presentations can be quite enlightening, since you ideally should know what you're talking about. Granted, I think it's easier to talk to non-specialists because then you can get away with more handwaving, but sometimes, when you want to explain stuff in the most basic way possible, it requires you to think things through - what's really going on in this process I'm trying to describe? How can it be explained in plain words?

There are some of things I loathe when it comes to listening to a presentation:

• Slides containing walls of text

Like this

• When the slides are exact copies of the speaker's manuscript
• When the speaker provides too little background. I would rather hear things one time too many than one time too little.

I therefore try to heed these problematic points when I make presentations, and I work by the following guidelines:

• I view slides not as the main conveyors of information, but rather as a tool to complement what I say. What I say is the most important thing in a presentation - not what's on the slides.
• I try to illustrate my points with pictures when possible - it's much easier to grasp and you don't have to read while the presenter is talking
• When I have to resort to text, I try to keep it as short and simple as possible. The slides provide cues for what I will say, but they're only cues, not manuscripts.
• I try (time permitting) to provide as much background as the listeners need to understand what I'm talking about.

The last point of course requires you to know your audience. My audience yesterday was quite varied in terms of background - some understand math, some don't. I wanted to explain a little bit how we analyse data in my field, which required me to explain Fourier decomposition and power spectrum analysis to the audience. I didn't quite succeed, even if I did it as basic as I could. However, the more math-savvy parts of the audience grasped what I said. So it would have been a choice between just dropping my goal of explaining what we do, and having a section of the talk being unintelligible. My choice was the latter even if I didn't know that's what I chose.

As for choosing the style of your slides: sometimes I think certain slide styles can look cool, but elaborate slide designs can sometimes take focus away from what you're saying. I use the Latex beamer class with just a very clean setup for my presentations.

Context in grading

This is another grading-related post, but it's also about context, which is one of my favourite terms.

I believe context is extremely important. Understanding context is what keeps humans from being machines. I think at least eighty percent of interpersonal conflict comes from disregarding or misunderstanding the context. Probably I will say something on this later.

But this post will be on context when grading. I don't have that much to say on the topic, but I needed to point out that when you grade exams, the ultimate goal is to assess whether the student has grasped the curriculum or not.

A person who is bureaucratic by nature (i.e. has a tendency to ignore context) will simply look at whether the student has written down the correct answer (in the natural sciences, that is). If it's not on the paper, it is irrelevant for the grading process.

And by doing so, the bureaucrat has failed to accomplish the goal of grading - namely to assess the student's grasp of the curriculum.

That is because what is written is not the only source of information available to the grader. Being a human, the grader also has access to the context of what is written.

As an example: If a student, during an explanation of some kind, uses the wrong word for a key term, the bureaucrat will automatically see that as an error. Don't get me wrong - it might be an error, but only insofar as it demonstrates a lack of understanding by the student. How to we ascertain this? By examining the context. If a student otherwise clearly shows what he/she is talking about, demonstrating an excellent command of the subject matter, then this error in wording shouldn't be taken as a symptom of lack of understanding, but simply as a symptom of momentary forgetfulness. However, if, along with this error, the student writes an explanation which shows that he/she has just been memorizing the curriculum, not really understanding what is going on, the error can be taken as a symptom of lack of understanding. In other words, the context determines whether this error should be penalized or not!

More on context later.

Healthy eating

Staying in shape can be tough when you're a desk-worker like me. I try to regularly exercise three times a week, and since anecdotal evidence suggests that you can't outrun your fork , I also try to eat healthy. 

Which means I won't be able to do this anymore.

I have no zen tips for accomplishing that. But once you start to actually see the contours of those abdominal muscles you thought were dissolved in fatty acids, you start to understand what Kate Moss meant when she said "Nothing tastes as good as skinny feels". Not trying to condone anorexia here, obviously. I am currently in no danger of having that condition.

Another thing that has been important for me to keep in mind is that being hungry for an evening isn't dangerous. Going to sleep hungry isn't going to kill you. And usually you're not really hungry either, it's mostly just being half-full and/or bored.

A third important thing for me is not to fail miserably once I fail. As Jillian Michaels said: "Think of your weight loss journey as a car. If you were driving along and got a flat tire, would you slash the other 3 tires and call it a complete loss? No. You would fix that one tire and keep going."

There is one way of thinking within the fitness world that I simply find to be impractical, and that is the thought that you should eat often and eat small meals. The reason I have a problem with this is that it's thinking about food that makes me want to eat. The less I have to think about food during one day, the less I feel the need to eat. Thus, I limit my meals to three a day, and once I have finished one of them, I know that I won't be eating again for a while. And usually my stomach then tells me when it's time again.

Motivational quotes get a lot of heat from the irony generation. But I find them to be useful - they're like someone jerking your shoulder when you're about to fall asleep. Maybe I'll do a compilation of my favorites one day, for the pleasure of all my imaginary readers.

Assigning grades

In my series of extremely interesting grading-related posts, I want to raise a question about the assignment of grades.

Namely, how on earth are you supposed to assign grades? The ideal, at least in my institution, is that the grade distribution should be Gaussian after removing the fail grades. So far, there are three "schemes" I can think of:

• Giving grades based on some "objective" scale - i.e., if students get ninety percent or more correct on their exam, they get an A, a B if it's between eighty and ninety, and so on.
• Total relative adjustment of the scale: The top ten percent of the students gets an A, the next twenty percent gets a B, and so on.
• A "hybrid" solution. You find natural cutoff points that are not too far away from the "objective" scale so that the number of people who get an A and so on are approximately correctly distributed.

The first option is the most ideal one. It is also the one most likely to give rubbish results, the reason being that there is no such thing as an objective scale. First of all, an exam is in itself a random sample of questions based on the curriculum (at least in the natural sciences), not a complete assessment of the knowledge of the student. Second of all, what the teacher thinks the students should know is not what the students actually know. Sometimes a question is harder to answer than the teacher thought. To think that an objective scale like that can actually exist is naive. Finally, unless the teacher is actually the perfect intellect, the resulting distribution won't be Gaussian. I will concur, though, that in the case of social sciences and the humanities, where the exam's score isn't as easy to determine in terms of right/wrong answers, this scheme might be preferred. Also, in low-attendance courses, it might also be possible to actually take the time to give a well-founded total percentage instead of just averaging over the percentages per question.

The second one is the most appealing to me, at least when the number of students taking the course is large, which is when you would expect something like a Gaussian distribution anyway. The main criticism against this scheme is that the grades become relative, so that an A one year is different from an A the next year. I posit that this is a problem with all of the above schemes. The "objective" scheme will be subject to variation because the teacher is not God, and because you typically don't give the same exam year after year. There is a point at which the second scheme will give larger variations than the objective scheme, but as long as the number of students are high, the total relative adjustment scheme will be more robust than the objective scheme.

The third option I think is an ok compromise if you feel uneasy about the total adjustment scheme. I dislike it because of its non-automated nature - i.e. even once you have assigned a percentage to an exam, you still have to make subjective judgements. Also, it seems to me this method is prone to even more arbitraryness than either of the two previous ones.

It is worth to note that most grading systems explain grades in terms of level of understanding - i.e., an A means that "the student has an excellent command of the subject" etc. In these terms, the objective scheme is the preferred one - there should be no a posteriori tinkering with the results based on the distributions! However - it's impossible to a priori know where to draw the line. If you say that an A should be ninety percent correct or more, then you might end up with no students getting an A because your standards were too high. You might say "well, that's too bad for the students - we cannot lower the bar just because the students do badly." But the point is that you don't know whether you're lowering the bar, because the concept of an ideal 'objective' test is flawed from the outset! If you base your grades on the actual empirical distribution, there still will be incentive for students to do well, because only the best ten percent of them will get an 'A'.

Ideally, then, one should change the whole meaning of the grading system. Instead of saying that grades reflect some kind of absolute skill level (which is a flawed concept anyway, unless you spend extreme amounts of time or unless the number of students is low), the grades should simply reflect which percentile you ended up in. I.e. an 'A' should just mean that the student was among the top ten percent of the class, and so on.

I'm not sure yet what we'll end up using for these exams, although we have used the third approach before. If I have the time, I will write some code to do some statistics on the results of this one to see if there are interesting patterns to be found.