One Quarter Down.

Straight A's!  Well, three A's and an A−.  Consequently, I'm feeling smug.

Bring Back the 15c!

Well, that last post got me nostalgic, and now I discover there's a web petition to bring back the HP-15c. I used to have one, and wish I knew where it was. I searched for it a few years ago, but I guess it's gone, which is a pity, since it was kind of cool in its day and has appreciated in value since HP stopped manufacturing it&emdash;how many pieces of computer equipment of any kind can you say that about??

One thing I remember about it was its (then) unique ability to work directly with complex numbers. To do this, it had, alongside the standard x, y, z, t RPN stack, a parallel "imaginary stack" to hold the i components of the complex numbers. You could get to it with the fancy Re⇔Im button, which would exchange the contents of the two stacks. Trippy.

The Operator of my Pocket Calculator

I have to say, it's a little unsettling, having to study for finals at my advanced age. The first was today, and then two more tomorrow; and I did two take-home finals, so it's been a pretty interesting week.

Today's involved a lot of linear algebra, basically finding e^At, working with Laplace transforms and their inverses, Smith McMillan canonical forms for polynomial matrices, etc. And through all of this, I would have been absolutely sunk without my TI-89.

This brings back memories. Back in high school, I was the proud owner of what, at the time, was probably the most sophisticated hand-calculator made, the HP-41C. I could go on and on about it: it had some alphanumeric capability, it had a fair amount of memory for programs (basically sequences of simple instructions that worked with data on the stack), etc. You could add plug-in memory modules, and a variety of other little gizmos (including a bar-code reader). It certainly threw my first serious calculator, which I got when I was 13 or so, into the shade. (That was an HP-33C. It was programmable too, and I spent a lot of afternoons making it do little mathematical things. You are probably not wondering whether I was "cool" in high school, are you? Plus, I've dated myself. When I got the 33C they had just been released).

Needless to say, I was an HP snob; I was comfortable with RPN from day 1 and felt better-equipped than those who were forced to suffer with lesser calculators, typically the TI.

Well, times change. It seems to me that HP is basically out of the advanced calculator market. Yes, there's the HP-48, but there is no comparison to the TI: the TI pwns in all categories. Determinant of a matrix with symbolic entries? Check. Partial-fractions expansion of a rational function? Check. How about taking the limit of a matrix with symbolic entries? Unbelievably, yes: one step in constructing a minimal realization for a dynamic system involves evaluating lim_s→λ(s-λ)H(s) where H is a polynomial-matrix-valued function of s. And the TI can do it. If HP ever makes a calculator that can perform like that, I'll give it a try, for old time's sake; HP got me through high school and college.

I didn't like buying the TI, and there are a few things about it that irritate me, but over this last quarter I've come mightily to appreciate it!

Coated a Penny in Zinc

My fourteen year old daughter has recently been pestering me to do a chemistry experiment with her, that she can take to class. According to her, the science teacher refuses to do any experiments of her own, because the boys in class are too rowdy and she fears for her pupils' safety. (What's up with that?)

Now, I was good at chemistry, back in the day, but I have forgotten just about all of it. "How about baking soda and vinegar?" I ask. "We've seen that," she says. I think about it for a while and decide to try to electroplate a coin. When I was in high school we had silver nitrate, which was cool, but I'm not certain I can get a hold of that easily. Eventually I find this useful site, with a couple of simple experiments (and a lot of good safety advice, too: such as using Epsom salt rather than table salt to avoid generating chlorine gas).

So I'm at the hardware store buying zinc nails, a dry cell, some wire and alligator clips and I remember to ask if they have muriatic (=hydrochloric) acid, which one of the user-submitted experiments recommends, and I get the Perry Mason^* face from the local hardware guy. "What do you want that for?" I'm not kidding: exactly that face. Well, I guess you can get into a lot of mischief with hydrochloric acid, but nobody seemed to worry about it much when I had to use it to keep the pH of the swimming pool balanced when I was a kid. Oh, well.

I skipped the muriatic acid and made do with vinegar as the simpler experiment suggested. Vinegar, Epsom salt, copper, zinc and a battery. It worked.

^* I stole the idea of the Perry Mason Stare from Lileks.