Overheard on a TV commercial

Dialogue from a TV commercial Cathy just told me about:

"This checkbook just won't balance!"

"Well, no wonder! Look at the size of our utility bill!"

Since when does the size of your bills affect whether you can add and subtract correctly?

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Closing out the month

I'm going to end the June notebook now and spend a few days on other things. In the meantime, let me extend best wishes to my niece Stephanie Glisson and her fiancé Don Joyner, who are getting married on Saturday.

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Real estate slump? What slump?

According to Zillow, the value of my house, like that of many houses in Athens, Georgia, has been shooting up. Mine has allegedly been rising at 5% per month for at least two months. We make jokes: "They saw that we got the grass mowed!"

Here's an adaptation of one of Zillow's graphs, showing a 42% rise in 5 years:

This doesn't particularly do me any good, since I'm not planning to sell the house, and if I did sell it, buying any other comparable house would cost just as much... but at least it looks good on paper. And my taxes are presumably going up.

Meanwhile, as you may have heard by now, economist Paul Krugman has argued in the New York Times that American public policy shouldn't push people so hard to buy houses (see discussion here).

By equating home ownership with "the American dream," we have prevented people from moving out of declining industrial areas or (now that gasoline is expensive) areas with excessively long commutes. And we have made everyone a real estate investor and hence, nowadays, in many places, a losing investor.

Not everybody needs to own a house. Rent money is not necessarily wasted — you don't build equity, but you don't get tied down either.

The oddest objection I've heard to Krugman's argument is that "renters don't pay property taxes." Of course they do. Through their landlords!

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How to choose N items randomly from a given set

Suppose you have a set of items — in my case, lines of a text file — and you want to select a given number N of them at random. For example, suppose you want to choose 50 out of a set of 100.

It's not enough to just go through the set of 100 and have a 50% probability of taking each item. That's easy to implement, and it gives you about 50 items. But what if you want exactly 50, chosen at random?

An algorithm for doing this is given in Knuth's Seminumerical Algorithms, one of the Great Books of computer science, but in my opinion Knuth's presentation of it is — dare I say it? — clumsy by today's standards. He has a bit too much arithmetic, and one of the steps (incrementing the number of items processed) is done on both branches of a conditional.

On page 142 of the third edition, we read:

This obviously dates from pre-structured-programming days. Let's modernize it.

The key idea is very simple: Keep running totals of how many more items you need and how many items you have left.

For instance, if you needed 50 out of 100, and the randomizer told you to skip the first item, then now you need 50 out of 99. On the other hand, if the randomizer told you to take the first item, then you subsequently need 49 out of 99.

So at every step, you adjust the randomizer so that the probability of taking the next item is (number needed)/(number left), such as 50/100, 50/99, or 49/99 in the three examples I just mentioned. That is easy. Just generate a random number from 0 to 1, and take the item if the random number is less than the desired probability.

When number needed gets down to zero, you get to stop. If you go along without taking enough items, eventually (just in time), number needed will equal number left and you will take all the remaining items.

So here's the algorithm, expressed my way:

int nAvailable = the number of items in the set;
int nNeeded = the number of items to be selected;
while (nNeeded > 0)
{
    if (random() < 1.0*nNeeded/nAvailable)    // use floating-point division!
    {
        take the next item;
        nNeeded = nNeeded - 1;
    }
    else
    {
        skip the next item;
    }
    nAvailable = nAvailable - 1;
}

The expression "random() < nNeeded/nAvailable" can be changed to "nAvailable*random() < nNeeded" if your computer does multiplication appreciably more quickly than division.

There. That's today's contribution to computer science. I'm sure I'm not the first person to do this; the algorithm is a fundamental one and numerous programmers must have used it.

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Curious point of etiquette

We are now being told that it's rude or insulting to offer too little money for a house that's for sale.

That's news to me. I wonder if it's true. And if so, whether these people realize that by "feeling insulted," they are failing to sell their houses?

I would have thought that the proper response to an excessively low offer is to turn it down! That's how a market operates, folks. A "lowball offer" may be unrealistic, it may be annoying, but it's not insulting. If all the offers are lower than you expect, reconsider your asking price.

Or is this propaganda from the same kind of people who tell us we're rude if we don't lavishly "tip" the garbage collectors?

Of course, you could announce that your price is firm and that you won't consider lower offers (which is how retail stores operate). Or, if you wanted to be slightly whimsical, you could announce the minimum offer you would consider. Then that is the only amount anyone would ever offer you.

Putting that another way: If the rules of etiquette say, "You must never offer less than 80% of the asking price," then the rules of economics say, "You must never offer anything but 80% of the asking price."

The path out of the housing slump has to involve lowering the prices of houses that aren't selling. Your house isn't "worth" any price that people aren't actually willing to pay.

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M57 in moonlight

To try out the Canon 20Da, I photographed the Ring Nebula even though the full moon was rising and the sky background was very bright. This is a stack of 1-minute exposures taken through a 300-mm lens at f/5.

Addendum: As you may know, the Canon EOS 20Da is no longer made. The main reason this one is being lent to me is that it's no longer needed for advertising. I hear, though, that people at the Midwest Astro-Imaging Conference are clamoring for Canon to make a new 20Da (40Da, anyone?). I'd like to add my voice to the clamor!

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DSLR sensor cleaning

I had to clean some dust of the sensor of a DSLR this evening (June 19), and the usual puffs of air from a big rubber blower weren't sufficient. I didn't want to use "canned air" because it's too forceful and can cause damage.

Instead I used a Green Clean swab kit, purchased (without the "vacuum" kit, just the swabs) at Wolf Camera. (Here's the link to buy it from B&H.)

It worked well. There are two swabs, one wet and the other dry. They don't rely on evaporation to remove the liquid — instead you get to wipe it off.

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Miscellany

Anyone who reads this Notebook will notice that I seldom mention people by name unless of course I'm referring to something already known to the public. This is not a "web log" in which I tell you every trivial thing my "friends" have done. I respect their privacy.

Here is a nice piece by Jim Mischel on why every open-source software project has a benevolent dictator. You can't have a team without a captain. Participants in a project are not equals — somebody is the leader.

End of the ISA era: I felt surprisingly sad after scrapping Frankenstein the computer, and on reflection, I think I know why: For the first time in 10 years or more, there is no longer an ISA-bus computer on my workbench for experimentation. That means I no longer have a computer that (1) is easy to program with familiar software, and (2) has an easily accessible bus architecture. Back when I was writing the "Q&A" column for Electronics Now, I built an ISA card from scratch, just to show I could do it. It contained a couple of chips to decode a particular port address and perform input and output. We can't do such things with the PCI bus; each card has to have a little CPU of its own to identify it. An era is over (although I actually do possess two working ISA-bus computers; maybe Frankenstein will rise again).

And now I want to rant against ranters: As far as I can make out, newcomers to Usenet pressure each other to:

• Disparage Microsoft and especially Windows Vista;
• Rant against top posting.

Online discussions of Vista are frustrating because of their low information content; people bash Vista because they feel they are expected to, not because they know much about it. And the rants against top posting come, I think, from people just imitating other ranters who are trying to pass themselves off as Elders of the Internet. It gets tiresome.

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There is no privacy on the World Wide Web

Here and here are two timely warnings by Jim Mischel, addressed to people who don't realize that when you put something on the Web, everybody can read it and preserve it, not just the people you imagine are reading it — and even if you take it down, there will be backup copies preserved elsewhere forever.

By "Internet" of course he means "World Wide Web." Other Internet functions, such as VPN communication, are quite private.

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Miscellany

Things I've learned recently, No. 1: The distinguished computer scientist Brian Kernighan pronounces his name KERN-i-HAN, not KERN-i-gun.

Things I've learned recently, No. 2: You've heard of Martin Luther's "Diet of Worms," i.e., his trial, in 1521, in Worms, Germany. Well, all this time I thought Diet was a word awkwardly imported from German.

No; in Scotland and some other places, it denotes a day's session of a court, and in Germany, judicial and legislative sessions even if they a lot longer than one day. It's a genuine English word and, in this context, translates German Reichstag (which literally means "realm's day"). But Worms is indeed a German name, pronounced "Vorms."

Etymologically, diet comprises two words with the same spelling and pronunciation but different origins. The more familiar one is from Greek diaita "way of life" (including eating habits); the judicial one is from, or at least influenced by, Latin dies "day."

In other news: A Canon 20Da camera has come to visit me again, courtesy of Canon USA, and this ensures that we will have cloudy weather the rest of the summer.

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Flurry of activity

Everybody must have decided they'd resume doing things after June 15. Suddenly everything is happening at once, and this Notebook may be rather sparse for a while.

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Three minor disappointments

(1) Frankenstein is dead, of an intermittent connection on the motherboard, and has been scrapped.

(2) My ASUS P4PE motherboard only supports 1 diskette drive. I tried to put Frankenstein's 5 1/4-inch drive into Minerva (my main desktop computer) and was confronted with this unpleasant fact. Is there a workaround in Windows? There is definitely no BIOS setting to enable a second diskette drive.

(3) Some VGA cables have too many pins. Specifically, a connector with all 15 pins present will not plug into some older VGAs, including that of the IBM PS/2 Model 70 (another of my old computers that I was checking out briefly). Fortunately I found a different cable with the appropriate two (?) pins missing.

Nonetheless, I had a good Father's Day, largely cleaning up my workshop.

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Oddest thing I've found wrong with a computer lately

I have a computer I call Frankenstein because it's made of the cast-off pieces of other computers. It has an IBM 486SLC CPU, a Sound Blaster 16 SCSI (which is a soundcard with a SCSI disk adapter built in), and other odd components, all ISA bus. It serves as an operating-system zoo, booting DOS, Windows 3.1, Windows NT 4.0, or OS/2 as the case may be. It's on our Ethernet and may one day be used as some kind of server. With only 16 MB RAM, it won't run any current UNIX-like OS unless I make a really cut-down version.

This evening (June 13) I switched around some old monitors and put a different one on top of Frankenstein.

And then Frankenstein became unreliable. He started rebooting every few minutes, spontaneously, and then got to where he wouldn't reboot at all.

Fearing the worst, I opened Frankenstein's case and decided to start removing unnecessary components one by one. I started with the 1-GB SCSI disk drive and — lo and behold — a Y-cable supplying power to disk drives had come apart. A yellow terminal had come out of its plastic cover and was free to flop around. Apparently, when I jostled Frankenstein while moving the monitors, this yellow terminal, connected to + 12 volts, had come into intermittent contact with something grounded. Reboot.

So now, as befits a computational misfit, Frankenstein has been repaired with duct tape (well, with electrician's tape) and is running just fine.

Update: That didn't cure it for long. More checking to do... It's probably the power supply.

While I'm talking about old computers... does anybody have any ideas about how best to use an IBM PS/2 70 (386 CPU, 4 MB RAM)? And I don't mean as a boat anchor...

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Does AT&T block BitTorrent?

Does AT&T block BitTorrent? They say they don't, but whenever we've tried to use it, our network access slows to perhaps 1% or less of normal speed.

BitTorrent is a file sharing protocol. It has gotten a bad reputation because one of its main uses has been illegal sharing of copyrighted material — but abusus non tollit usum. An increasing amount of legitimate material is being distributed that way, and I rather regret that large-scale legitimate usage of BitTorrent didn't appear in its early days; the wrong kind of usage built its reputation.

A more serious objection is that when you download, you must also upload, and that can clog a network. (It also introduces an element of freeloading that is unsuitable for commercial products, in my opinion. Manufacturers should have us download from them, not from each other.) But I now think the clogging we have observed may be artificial.

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Tiny, cheap PCs

Gadget of the day: the eBox 2300, also known as the MicroClient Jr. This is an under-$200 personal computer that is good for controlling gadgetry. Information here, here, here, and here. I don't have one — probably don't even have time to do anything with one right now — but am intrigued.

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Has anyone seen this Macintosh problem?

Mac Mini, recent version MacOS, running Microsoft Word 2002. Occasionally, Word stops accepting input from the keyboard, and I have to use the mouse to save and exit, then restart Word.

Does this ring a bell with anyone?

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Vive la Picardie

The famous Duralex Picardie: I'm doing a consulting job in an office where we have bottled water from a cooler, and durable European-made glasses to drink it out of. The first time I saw one of the glasses, I wanted to say, "You're in the wrong country and the wrong century," because it was just like the glasses that were used universally in Oxford and Cambridge dining halls in my student days.

It turns out that the Duralex Picardie drinking glass is hailed as one of the great artifacts of the 20th Century and is no longer available because Duralex is out of business or nearly so.

Fortunately, they are still available secondhand. For complete authenticity, one wants the 25-cL (250-mL, 8.5-ounce) size with the round trademark that says "Made in / DURALEX / France" rather than the more subdued labeling of newer varieties.

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Economic matters

Here is an economist who argues that gasoline should be even more expensive to force conservation. The price will rise to whatever the market will bear, anyhow. Why should we send money to the Arabs when we can recirculate it in our own country?

Meanwhile, the new water conservation policy for our fair city (Athens, Georgia) deserves to be in economics textbooks as a bad example. They've set up sliding-scale pricing — but your quota of cheap water depends on how much water you used in the winter of 2006. Not the size of your house, or the number of people in it, or any indication of real need.

The result? They've made a policy that looks socialistic on the surface but actually subsidizes the rich. People with big houses and wasteful habits get more water at the lower price. The squeeze is on people who were already frugal in 2006, or who have children in college (absent in the winter, present in the summer), or who have newborn children.

The right-wing solution would be to price water whatever it actually costs, and let the market take care of conservation. The left-wing solution would be to give people a quota based on their actual need. Our county commission went out of its way not to do either one.

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M13 in all its splendor

This is the fruit of my labors — the sigma-clipped average of nine 3-minute exposures of M13, minus the sigma-clipped average of 10 dark frames. Canon 40D, 8-inch telescope at f/6.3. Stars are visible at least down to 17th magnitude.

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Adobe Updater crashes Windows Vista

Just now, Adobe Updater insisted on running, and then it said it needed to reboot my computer in order to finish, and when I rebooted and logged in, I got a pop-up that said, "Windows has blocked some startup programs" because the updater wanted to do something that required my permission, and then Windows Vista Ultimate crashed with a blue screen.

Fortunately, when I rebooted again, I was able to click on the pop-up and allow Adobe Updater to run.

I blame Adobe here, not Windows. As far as I can tell, Windows was performing as documented and Adobe Updater was doing something out of line. Windows Vista forces programmers to come out of the Windows 95 era. Under Vista, it is mandatory for software to respect the security of the system in ways that have been strongly recommended since at least Windows 2000.

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M13 and a satellite

This is what happens when a man-made satellite passes in front of a globular cluster while I'm photographing it. The cluster is M13; you're looking at a single 3-minute exposure through an 8-inch telescope at f/6.3. Later I hope to show you a stack of nine or ten such exposures, and because the computer rejects highly deviant pixels, the satellite track will vanish when the pictures are combined.

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The globular cluster M5

Here's a somewhat imperfect view of the globular cluster M5. I was having trouble with my autoguider and didn't get a set of sharp images as I was hoping; this is a single 3-minute exposure with no dark frame subtraction. Canon 40D, 8-inch telescope at f/6.3, in my driveway.

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The price doesn't go down until you ask for it

The cost of my web hosting at Sectorlink just plummeted to about 1/3 of what I had been paying. But it would not have done so if I hadn't looked at Sectorlink's current price sheet and realized that I didn't need to go on paying the old rates.

The cost of web hosting is plummeting, but if you keep renewing the same old account, the price will stay the same. Instead, I "downgraded" to the cheapest currently available account that will meet my needs. Presto — lower prices!

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Back soon...

My day job is keeping me very busy. Come back in a day or two and there may be some astrophotos here...

In the meantime, if you haven't discovered Glasbergen, do so!

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IDE solid-state disks

Gadget of the day: IDE flash memory modules (disk-on-chip modules). (See these too.)

Each of these is a small module that plugs into an IDE socket on a PC motherboard, where an IDE drive cable would normally go. Using the same type of solid-state memory as camera memory cards, it emulates a disk drive. You can boot from it. Embedded PC systems (those built into other machinery) often do.

I'm tempted to buy a few and make something — I'm not sure what — out of some old computers.

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Bifenthrin

[Revised June 12.]

An essential part of amateur astronomy in Georgia is mosquito control. I used spray cans of Yard Guard until I learned, more than ten years ago, that its active ingredient, permethrin, can be bought much more cheaply as an almost odorless concentrate to mix up and apply with a sprayer. So now I spray my yard for mosquitoes periodically, taking care to hit the undersides of leaves, where mosquitoes rest. Often I do a light spraying of fine mist just before setting up the telescope.

This year, Ortho's lead product, Ortho Max, uses bifenthrin, a different but related chemical. Like permethrin, bifenthrin has low toxicity to humans and most pets, though it is toxic to fish. Both of them are synthetic chemicals that resemble a natural insecticide found in chrysanthemums (pyrethrin).

From this article I learn that bifenthrin is about ten times as potent as permethrin; that in doses too small to kill mosquitoes, it prevents them from biting; and that it is less irritating to them (meaning they don't fly away as quickly when they land on a drop of it — and this is said to be a good thing). It's also less irritating to human skin.

I'd like to hear from people with expert knowledge of permethrin vs. bifenthrin. In particular, granulated bifenthrin is sold for killing ground insects, but not mosquitoes; would it help keep mosquitoes from nesting in the grass?

[Update:] After some experience in the field, I think bifenthrin is not as good as permethrin for my purposes. Bifenthrin apparently kills more slowly and does not repel the mosquitoes. These attributes are probably advantageous if the goal is to eradicate a population, but I'm generally wanting mosquitoes out of the way now when I'm setting up my telescope. Ortho "Total Kill" is still permethrin.

I know there are people who believe that, on environmental grounds or for the sake of human safety, we should never use insecticides. My reply is that mosquitoes are not just annoying, they are genuinely dangerous, carrying West Nile disease, encephalitis, and other hazards to human health. Also, in Georgia we're not talking about just a few mosquitoes; they're numerous enough that an unprotected individual could get hundreds of bites in one night. In my opinion, killing mosquitoes with pyrethroid insecticides is less dangerous than letting them bite people.

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There is no such thing as "identity theft"

I reject the notion that I have a possession called my "identity" which other people can "steal."

If someone walks into the local Bank of America branch, pretends to be me, and persuades the bank to give him money from my account, who has been robbed?

The bank, of course, not me. It's the bank's job not to give my money to impostors. This hypothetical thief hasn't stolen my "identity." He hasn't even stolen my money. Not even if he robs ten banks, not just one, using my name.

The financial industry, of course, would like us to think that impersonation or identity fraud is the victim's fault, or at least that the impersonated individual is the victim. I reject both of these propositions.

And it looks like the Federal Trade Commission is starting to agree with me.

A related point that I had to keep hammering home, ten years ago, is that there is no such place as "cyberspace." Have you noticed that people have finally stopped talking about "cyberspace"? Maybe, eventually, the misleading term "identity theft" will go away too.

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