Martin’s Blog

Blog
About

Running byes straight to the wicketkeeper

September 30, 2009 at 9:21 am | In Cricket | 5 Comments

We once again* saw an international cricket team have no idea what to do when the score is tied with one ball to go (actually Younus Khan looked like he had no idea what was going on at all).

*England had a whole over of missing easy runouts against The Netherlands, I think, in the World T20. That may have been Stuart Broad at the bowler’s end but the same principle applies.

Some simple ideas:
- wicketkeeper up at the stumps
- if you can’t do that, train your keeper so that he can hit the striker’s end stumps 3/4 of the time
- if that doesn’t work, have a short leg there to receive the ball
- also have a short midoff to receive the throw to the other end to prevent the delayed steal*

*This would work, right? The non-striker takes the absurd lead he is allowed under current rules and then the striker waits until the non-striker arrives before setting off on the run. There’s no way to get an out at the striker’s end.

Your team needs to practice this for about 15 minutes once and then they’ll know what to do.

Animated gifs

September 28, 2009 at 5:39 pm | In Mathematics | 3 Comments

You might say that I could have spent my time better but after a few hours of work I was able to make this rather inscrutable picture. Any guesses as to what it’s doing?

Hi Dave!

Shane Warne

September 13, 2009 at 5:48 pm | In Cricket | 3 Comments

With my recent thoughts and endeavours not leading to interesting blog posts (even by the low standards of this site) I will merely give you a youtube video of Shane Warne.

Later in his career Warney was ‘just’ an accurate bowler of legbreaks that turned enough to be dangerous who also had a psychological hold over batsmen and umpires. But circa 1994 he was an absolute bamboozler – the flipper especially was unplayable for people that grew up in South Africa, England, West Indies…

This video from 1994 against South Africa is worth watching:

Quiz answer & discussion

September 3, 2009 at 2:16 pm | In Mathematics | Leave a Comment

1/3 is ‘correct’ by exactly Dave’s solution. I was going to provide a more detailed and motivated exposition but I don’t think I can be bothered. My knowledge of Bayesian inference comes exclusively from reading the first half of section two of McKay’s textbook Information Theory, Inference and Learning Algorithms so you can read that and know as much as I do.

So, points for Dave for doing what the book did, Yuliya for getting approximately the right answer first and Leesa for having both the worst and possibly the best answer.

The answer of 0.3 is clearly terrible: if you are a frequentist that doesn’t believe in probability representing belief then your real answer should be that the 10 flips are not at all significant.

But the 0.3485 might be pretty good. What was your prior Leesa? I can certainly believe that a prior that is normal with mean 0.5 and some smallish standard deviation is perhaps more reasonable than a uniform prior and that should give us an answer above 1/3.

A quiz

August 31, 2009 at 8:47 am | In Mathematics | 9 Comments

You toss a (not necessarily fair) coin 10 times and get three heads. What is the probability of getting a head on the next toss?

Guesses and answers with some calculations are both acceptable.

The argument of a complex number

August 30, 2009 at 12:56 pm | In Mathematics | 3 Comments

The argument of a complex number is defined to be a number $-\pi <\theta \leq \pi$ which represents the angle of the vector corresponding to the number measured from the positive real axis. If you draw a picture of this setup your first thought is that $\theta=\arctan(y/x)$ . Unfortunately this can't work because the range of $\arctan$ is $(-\pi/2,\pi/2)$ . It is true that $\tan(\theta)=y/x$ but ever since I learnt about complex numbers 8 years ago or so I just knew that you had to draw the picture and think about it to solve this equation for $\theta$ .

But just a few days ago I discovered* that there does exist a formula! (well, it can’t give you an answer of $\pi$ but apart from that it works). It is the rather mysterious statement $\theta=2\arctan(y/(\sqrt{x^2+y^2}+x)$ . Wikipedia says that it’s related to half angle trigonometry but looking at the formula you should also be able to get it from a picture of a circle.

*reading something on Wikipedia is a form of discovery, right?

So here’s one way to come up with it: Draw the point $x+iy$ in the complex plane and then draw the circle centred at the origin that goes through the point. Now consider the following diagram.

A circle

The angle at the boundary of the circle is half of that at the centre (that’s a theorem from circle geometry but it’s pretty easy to see from the picture in this case). The radius of the circle is $\sqrt{x^2+y^2}$ so you have $\tan(\theta/2)=y/(\sqrt{x^2+y^2}+x)$ and this time you can invert with the standard $\arctan$ function.

This seems quite weird to me: that this function works but the other doesn’t. It’s a stereographic projection I guess and $\theta$ is a better coordinate than $y/x$ …

This formula isn’t actually that useful but it was just what I wanted to find to do a question from my complex analysis homework 0, so it was helpful to someone somewhere.

It’s hard to take ratemyprofessors.com seriously

August 25, 2009 at 8:33 am | In Life in America, Teaching | 6 Comments

My two most recent reviews on my ratemyprofessors.com profile (a hugely biased sample of four students out of about 150).

Simply he’z a great teacher. he makes Calculus as an easy material you ever expected. Just study for review study and you’ll do fine. An A is acheivable since his exams is a pretty easy.

I sincerely hope that this student speaks English as a second language.

Martin is a mathematical genius. His stories of kangaroos killing people are funny too. The class is tough, tests are tricky, study and an A is achievable. Good teacher!

I don’t recall telling any stories of kangaroos killing people.

Also, if any readers want to add fake reviews (are those two above fake?) I’d appreciate one of those little chili pepper icons saying i’m ‘hot’.

My new favourite family picture

August 23, 2009 at 10:15 pm | In live music | 3 Comments

Well sure, it’s actually only got one member of my family in it…

My sister Ellen on the left, Tali White in the middle

The Lucksmiths played their last ever Brisbane gig later tonight*. Hope you enjoyed it Elle.

*grammar problems caused by the international date line

Bad predictions

August 22, 2009 at 3:28 pm | In Cricket | 9 Comments

After my last two cricket posts have shown my complete lack of predictive power (I thought Australia would chase 500 last time they had that target and that Stuart Clark should play over Hauritz) I should probably keep my mouth shut.

But I really think Australia has a chance of chasing a world record total this time. Somebody is going to do it some time and this Australian team is probably most likely to do it. They can score dominant test match centuries from 1-8 in the order and the pitch isn’t that bad…

So I’ll be waking up at 3 am tomorrow morning. Hopefully I won’t be going back to sleep at 4:30.

Dbacks commentators

August 16, 2009 at 8:46 am | In Baseball, Life in America | 1 Comment

Or: And you thought the channel 9 commentary team was bad…

Inspired by a comment on an amusing post from David Barry saying “Dodgers-DBacks coverage just started. The host has an excruciatingly slow voice. I hope he’s not the main game caller….” I need to vent my frustration with the two idiots that I have to put up with whenever I watch baseball.

But first, I should probably answer Dave’s question:
- If you were listening to the Dodgers’ feed* you heard Vin Scully. He does speak painfully slowly but is beloved in LA and the entire country. He’s been calling Dodgers games since they were the Brooklyn Dodgers in the ’50s.

*baseball games all have two feeds, one home and one away. And even if you pay to be able to watch every feed in the country you are blacked out of the other feeds for teams playing against the team(s) that you are in the home territory of. So I have to watch 150 games a year on Fox Sports Net Arizona. It’s horrible.

- If you got the AZ feed then the two main guys were away on Saturday (Mark Grace was on a nationwide Fox game and Daron Sutton was calling a high school game I think) so you got 2 of the backups. Last night it was Matt Williams and Greg Schulte. Matt Williams is also very slow and boring so it might have been him you heard.

But what really grinds my gears is the “Gracie and Sutt show” that the Dbacks broadcast often becomes. It’s a bunch of catchphrase based humour, out-and-out lies, forced hokiness and ignorant comments. Examples:

- Catchphrases: “that’s big league!”, “let’s get some runs!”, “big John Rauch”, “Jonathon Broxton, the biggest man in the world”, “big Adam Dunn”, “give that man a contract” (when a fan catches a ball), “car” (when there’s a break in play), “gas”, “we need more signs”, “right down broadway”, “letting it travel like Andruw Jones”, “that play hasn’t worked since Edner Doubleday was a boy”,
- sponsorship: the Aflac trivia question, the Qwest high speed internet high speed pitch, the Brown and Brown Chevrolet key to the game, the Taco Bell free tacos
- claiming that a players nickname is ’shoes’ when it really isn’t
- the kidcaster
- When the trivia question is asked either Sutton just looks up the answer on his laptop and ruins it for everyone or they spend about 10 minutes pretending to receive text messages from former dbacks players with horrible guesses in them
- arguing about which mascots are the best*
- mark grace saying that tacos with arms freak him out
- mark grace saying he prefers soft tacos

*actually this is quite interesting. I like Mr Met: he’s just a man with a giant baseball for a head.

It’s like Roy and HG but they’re serious and it’s not very funny.

Blog at WordPress.com. | Theme: Pool by Borja Fernandez.
Entries and comments feeds.