## Happenings Feb 27

Okay, it’s Saturday morning.

I’ve put in my hour of stream of consciousness, mostly about mathematics. My kid has had a shot at whatever he wanted to do. Late today I plan to work on the next color post; it should be a detailed look at the fundamentals and the residuals of four spectra. Before I work on the post, and after I finish this, I will do some mathematics.

Even I find it a little hard to believe, but I’m not actually sure what mathematics I am going to work on this afternoon.

My kid isn’t the only one who does mathematics for fun. The bottom line is that my grown-up does too. The difference is that my kid gets to have a little fun every day. That is, on the days I don’t do real work — although he’s been known to get in some at the end of a real work day.

My grown-up gets to just have fun when he runs out of steam on a particular subject –which is another way of saying, when that particular subject stops being satisfying. (it’s a little too much to expect everything I ought to do to be truly fun.)

It’s true that my grown-up has an agenda — but it is not carved in stone. I have no intention of putting myself in a straitjacket and saying, “Here is the mathematics you will do for the next month, or two, or six.”

I can understand that some of you wish I would pick up wavelets again. Some of you may be sorry to see me put down colors when I finish with them. While my grown-up wants to finish what he starts, it is for small values of “finish”. (Really. 52 posts on PCA/FA made me comfortable, a good start but could hardly be said to have finished the subject.)

I am not going to do color until I am an expert in the field. In fact, there are only two things left that I want to do.

• Get from XYZ to a spectrum;
• get from XYZ to RGB on my monitor.

Now, by the time I get through these two, I may have found something else I just have to do with color… but real soon now I will put down color and pick up something else.

As I did with wavelets. As I did with PCA/FA (principal component analysis/factor analysis).

I already have some mathematics done that I need to convert to posts:

• Logic;
• Stepwise regression;
• isolating multi-collinearity.

That’s good, because it will let me do some other mathematics without having to turn it into a set of blog posts right away.

Oh, I think I’m going to pick up orbits again. No, I haven’t done them yet on the blog — although I did talk about the orbit of Mars as an example of transition matrices.

Several years ago I did work out the orbits to get Mariner IV to Mars, and Voyagers 1 and 2 to Jupiter. What I want to do now is work out the gravitational assist for one of the Voyagers at Jupiter.

As for the past week, I have already altered the small pile of books on my smallest desk.

I like having it. It is a more potent reminder of the mathematics I want to touch than a written list would be. It also serves as a handy supply of quick reading material.

I grew up reading at the dinner table. I rarely sit down at a table to eat, at home; but if I go out to dinner alone, the first question is: what am I going to read?

“What am I going to eat?” is the second question. What kind of restaurant should I drive to?

Now I don’t have to walk into my library to find a book for dinner — my smallest desk has a perfect selection. Ah, I now have a reading menu.

I have, alas, added three books to it; on the other hand, I have removed one; and I have altered one. (And, of course, I just checked: there are 17 books there.)

I have removed Mermin’s “Quantum Computer Science”. Somehow, amidst the other books, it no longer looked as exciting as when it was sitting with the rest of my quantum mechanics books.

I have swapped out Skogestad & Postlewaite’s “Multivariable Feedback Control” and replaced it with

Blakelock’s “Automatic Control of Aircraft and Missiles” (biblio)

— because I think I can now derive what I consider to be its fundamental equation. I do want to return specifically to control of aircraft, and that to book in particular because it uses classical techniques. (I think of that as learning to shape wood using hand tools instead of power tools — power tools being analogous to state space techniques.)

• Guckenheimer & Holmes, “Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields”.
• Vetterli & Kovačevic’, “Wavelets and Subband Coding.”

• Armstrong, “Groups and Symmetry”.

Along the way, I decided to turn “the big three “into “the big four”. I have promoted “dynamical systems” from a subset of “control theory” (?!?) to a major group in its own right. In retrospect, I can’t imagine why it wasn’t always “the big four”.

So, I have selected four books for my smallest desk for each of the big four (dynamical systems, control theory, differential geometry, time series). What looks like a second book on differential geometry (Bloch, biblio) is, instead, a reminder that I really, really need to summarize his chapter 3.

There is nothing on that desk about color or logic; they are what I am actively working on, what I wake up dreaming about.

As for the blog itself, some of you may have noticed that I have made a cosmetic change to the bibliography. I wanted the authors names to pop out — because I think of most books by an author’s name rather than by title. I still wanted the titles to pop out, and I decided that I might as well use color. So now we have titles in red and authors’ last names in bold black.

I still need to go back and clean up the earliest entries on the bibliographies page. Some of them are just plain crappy looking. The key is that I have a better tool available than when I started.

I find that MacSpeech Dictate works very, very well — and although I have to specify the punctuation, it generally takes care of spelling and capitalization. I spend more than enough time hunched over the keyboard typing mathematics, latex, and operating system commands — at least I don’t have to type text.

You could hardly have missed that I have also made a cosmetic change to many of the posts. I have used the command “more” to display only an introduction rather than the entire post.

I don’t know about you, but I like that change. I like seeing 10 posts in about three screens now. I like seeing the context and history — and it makes it a lot easier for me to go back and find a particular post. (I do use my own blog for reference!)

I have not changed all of the posts — quite possibly less than half of them so far — but I’ll keep working at it. Oh, it also means that older pages load more quickly — unfortunately, I haven’t split all of the older pages yet.

Incidentally, the blog set a new record last Monday, 258 hits. Thank you.

Of course, my kid got to play before I drafted this. What did he want to do? I wanted to believe that he wanted to do orbits — but he knows perfectly well that my grown-up wants to do orbits, so he doesn’t have to. In fact, I think my kid is waiting to play with them after the grown-up writes a collection of functions to make it easy.

In the end, my kid actually looked at a EE book, to see how they presented Boolean algebra and what they wanted from it.

Okay, I need to turn this draft into a post….