### die throwing problem

Here’s a link to a subtle probability problem.

You throw a die until you get 6. What is the expected number of throws (including the throw giving 6) conditioned on the event that all throws gave even numbers?

### capital markets

QE3 was announced today and reactions have been relatively muted. There are some complaints that money is again being redistributed from asset holders to debtors via the mechanism of negative real rates. It seems like a good occasion to put forth two oddities that I’ve always seen as embedded in capital markets as they’re currently constructed. They are: the assumption that money doesn’t spoil, and the assumption of market optimality.

### two problems with win7

I finally had enough of two long-standing problems that bugged me in Windows 7, so I fixed them.

1. The ‘System’ process uses a low level of CPU (~6%) when nothing is going on.
2. Chinese characters in the system (e.g. file names) suddenly become boxes.

The first problem caused excessive battery drain along with the CPU fan going on and off all the time. Because Task Manager doesn’t tell you what is under the ‘System’ process, I had to use Process Explorer, which promptly identified the culprit: a revolving series of threads labeled ‘ntoskrnl.exe!KeReleaseInStackQueuedSpinLock+0x1e0′. This would appear to be some issue with a driver stuck on something and aimlessly retrying. It turns out turning off Wifi cured it. An updated driver for the Broadcom 4313 802.11n card fixed the problem permanently. The old version was 5.100.82.82 from 5/2011. The new version that does not have the problem is 5.100.82.112 from 10/2011.

The second problem is caused by a little-known new setting in Windows 7. Under Control Panel -> Fonts -> Font settings, there is an option “Hide fonts based on language settings.” It’s simply broken, so I just turned it off.

### phone vs. tablet vs. laptop vs. desktop vs. server

It seems that Microsoft’s all-in-one strategy on support for different devices is still progressing. Windows 8 will have interfaces for both the desktop and touchscreen devices. This is akin to how Windows Media Center works. This model must have an unusual level of attraction to Microsoft due to the large base of existing applications, but it makes assumption that you’d want to use all the applications on all the devices, if only you could — that may turn out not to be right.

Microsoft has for years tried to get into mobile devices. Here you see Bill Gates really uncomfortable with the notion that Apple has succeeded more than Microsoft in this space. He is not wrong, since for a time Windows phones and tablets were the only ones out there, while Apple’s Newton was forgotten memory. Those devices either used a slightly modified Windows OS or one that copied all of its metaphors. The latest Windows phones are an exception, but with Windows 8, it will no longer be. It cannot be disputed that there are important applications that do not exist on mobile devices (currently), and therefore mobile devices are not complete (currently). So people argue that mobile devices will be full-fledged computers or desktops will not die. The idea of a dual interface seems to be aimed in this direction. However, a third possibility exists. Applications, after all, merely solve real life problems. They are not themselves holy. If there were a different way of accomplishing the same things, the applications could be replaced. One could argue that data is the rather more holy object. Back to this later.

### risk matching in gambling

An argument for playing a game such as poker with “real” money is that it forces people to play with true risk-reward calculations. While this is certainly better than playing without risk, there exists the question of how to match risk profiles among players. With enough players (large liquid market), they can self-sort by stake size, and this seems fair. With only few people though, the situation is turned around, where a stake size has to be agreed upon at some clearing size (so that enough people agree to play the game) rather than chosen individually, and that same amount of money may be considered as very different values by different people. A pauper and a millionaire do not see \$100 as the same value, and will adjust their utilities accordingly, and this will materially affect wagering. Since risk is measured in utility units, it is desirable to match utilities rather than dollar amounts. But there isn’t an agreed-upon utility currency. Or is there?

### learning in social networks

There was this talk (by M. Dahleh) on modeling whether distributed learning occurs in a social network, i.e., is the crowd always right? The problem model was like this: there is a “truth” which is either 0 or 1, representing some binary preference. Then in a connected graph representing a learning network, each node makes a binary decision (0 or 1 again) based on an independent noisy read on the “truth,” as well as the decisions made by some or all of its neighbors who have already made a decision. (Each nodal decision is made once and binding, so there is a predefined decision-making order among the nodes.)

This is an interesting question because at first thought, one would think that in a large enough network, a sufficient number of independent reads on the truth will occur in the aggregate to allow at least the later-deciding nodes to get a really good estimate of the truth. This is the basis of the folk belief in “wisdom of the crowd.” However, this is not what happens all the time.

### double-sided usb

This design is pretty good, though it would probably break prematurely. Stuff that needs to be plugged in and out repeatedly maybe should not have moving parts. More to the point, why was USB specified to be one-sided in the first place? There are no two rows of pins like in some connectors, so there is really no problem with a receptacle having contacts on two sides.

### different kind of coupon collector’s problem

The classic coupon collector’s problem asks for the number of samples it takes to collect all coupon types from a sequence of coupons in which each of the $$k$$ types of coupons has an unlimited number of copies.

Here is a different kind of problem: if there are limited copies of each of the $$k$$ coupon types (say, $$d$$ copies), how many samples does it take to collect $$t$$ coupon types?

### stupid powerpoint

I ran into a problem with TeX4PPT the other day.

* As an aside, TeX4PPT inside PowerPoint is probably the fastest way to make scalable figures and math. There is just no way that any other drawing tool even comes close to the speed with which simple diagrams can be made using PowerPoint. Since the LaTeX people seem completely uninterested in the end user, there is basically no choice in the matter. My work flow these days involves LyX initial drafts with LaTeX final drafts for papers and PowerPoint with TeX4PPT for presentations, using pen input for the initial drawings. Not ideal, but getting there.

But I ran into a problem where every time I saved any LaTeX expression with the symbol $$\gamma$$, it turns into a degree symbol, that little circle °. It turns out $$\gamma$$ is codepoint U+00B0 in the font cmmi10. But PowerPoint’s default master template has gone stupid, and never wants to change the font type of just that one codepoint, so it goes with the Arial glyph there, which is the degree symbol. It doesn’t help that LaTeX is stuck in the stone age and doesn’t know about Unicode, instead using about 20 different fonts with overlapping codepoints to make the expressions.

So in the end I had to carefully recreate a clean master template in PowerPoint. For future use, it is saved here.