## Happenings – 2011 July 30

Let me start easy and warm up.

Thursday was a very surprising day on the blog. In 4 of the last 7 full days, I’ve had fewer than 100 hits; but Thursday had 230 hits – 51 on my home page (high, but not that unusual) and 49 on the 3–5–8 puzzle about splitting 8 gallons of wine into 2 four-gallon shares.

49 hits is unusually large for any single post. It may well be a single-day record for one post. I have no idea what caused that flurry of activity.

Since today is the final diary post for July, let me go way out on a limb and predict that there will be at least one earthquake of magnitude 7 or higher somewhere on earth in August. It would be more prudent to say one such quake in the next 2 months, but I’m bored from being safe with my forecasts.
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## Happenings – 2011 July 23

It’s been a distracting week, and I’m having trouble focusing on mathematics.

Last night, for example, I reread most of “Breaking the Maya Code”, by Michael D. Coe, a professor of anthropology at Yale, and curator of anthropology in its Peabody Museum. It describes how people learned to finally read the Maya hieroglyphs; unfortunately, this success was delayed for two generations because the great man in the field believed there was nothing to read, and his condemnations of people who disagreed with him were rather slavishly followed. (He believed the hieroglyphs were not related to any spoken language at all, never mind being related to spoken Mayan! Talk about putting a roadblock in the path of progress!)

It’s a good read, a popular book rather than a text.
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## Regression 1 – Multicollinearity in subsets of the standardized hald data

Edit: 8 Aug. Remarks added in “Regressions with no constant term”.

## introduction

It would be fair to say that this post is primarily for my reference, but it does provide a second example of looking at all subsets of multicollinear data.

As we originally did for the raw data, so for the standardized data: we looked at multicollinearity for the three regressions of most interest – namely, the best 2- and 3-variable regressions, and the all-4-variable regression.

Now, as we did for the raw data, so for the standardized data: let’s look at all subsets (of columns) of the design matrix X. (In fact, it is easier to look at the equivalent: all subsets of rows of the transpose of the design matrix, X’.

Nevertheless, let me summarize what we will find. You may not feel a need to look at the computations. I think at the very least you will want to look at the section on regressions without a constant term, and at the 3-variable subsets.
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## Happenings – 2011 Jul 16

The Blu-ray extended versions of the Lord of the Rings movies came out recently. A few friends and I are going to get together this morning, and we will start watching “the Fellowship of the Ring” at about 10 AM, on a very large HD TV. What with one long break in midafternoon, and small breaks during the day, we will probably finish “Return of the King” around 10:30 PM. (We’ve done this before.)

So, I will do no mathematics today… but I will be suitably geeky.

Offhand, I can only think of one other similar all day event. This isn’t possible for the Harry Potter movies, or for the six Star Wars movies – those both cannot be handled in a day, not by me anyway. And the original three Star Wars movies didn’t take all that much time to watch.
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## Color – RGB and XYZ on my monitor, again

I set out to do something very simple: let Mathematica do the transformations between RGB and XYZ. Since CIELab is defined in terms of XYZ, but my monitor (“Color LCD” on a MacBook) is RGB, I’d like to be able to convert between RGB and CIELab.

Well, I showed us how to convert between RGB and XYZ, in a previous post about the nonlinearity of my monitor.

Recall the purple disk that figured so prominently in that post. It was defined by:

$RGB = \{0.5666,0.3877,0.6864\}$

and drawn by Mathematica® as:

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## Happenings – 2011 Jul 9

It’s been a relatively slow week for the blog. Work has been busier than usual, and the temperature has been hotter than usual.

My earthquake prediction for July? On July 7 there was a 7.7 followed by a 6.0 in the Kermadec Islands Region – which is part of New Zealand, but about 550 miles northeast of its North Island. That gives me half of my predicted four earthquakes of magnitude at least 6 in July.

Here’s an odd picture of the location of the 7.7 quake.

The two big land masses are Australia to the left and Antarctica at the bottom. Clearly the USGS has software that rotates the globe so that the epicenter is dead-center.
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## Color: CIELab and Tristimulus XYZ

Let’s talk about CIELab. I’m not going to provide any background or discussion. This wiki article is an excellent introduction.

And there’s a very nice article about HSB. Furthermore, it includes an example with many more parameters than just hue, saturation, and chroma computed, which is outstanding. It also has a lot more information about HSI versus HSB; the differences seem to be more than I was led to believe from my previous reading.

CIELab is specified as a transformation from XYZ tristimulus coordinates. What motivated this post is that the only inverse transformation I’d seen published – until I read the wiki article – is incomplete. That’s a polite way of saying it doesn’t always work correctly. And that’s a polite way of saying it’s wrong.

In fact, the inverse transformation in the wiki post is perfecty straight-forward, and I’ll show it to you in more detail than they do.
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