## Happenings — Tag clouds.

This was intended as my first post after the long holiday layoff.

I know, it was more than two weeks between the last post in 2008 and the first post in 2009. Well, it was the holidays and the end of the year, and my annual letter to write, and there are still some football playoff games (as I draft this). (Go Steelers! Ah, only the Superbowl is left to watch. Except that I’m also a fan of Roger Federer, and there’s this thing called the Australian Open….)

You may have noticed that I have added a tag cloud. Once I found out how it could be used, it seemed like a very, very good idea. (I’ve gone back and checked my elementary book on blogging, and it doesn’t say a damn thing about tag clouds.)

I have gone back through the posts and added more tags to them. For example, now you can select all of the PCA/FA posts pertaining to Harman. That should be convenient, since the earliest post was about a year ago.

In addition, a search of a page includes searching the tag cloud, so if you search on “PCA”, you will find the tag “PCA FA principal components factor analysis”; this means I can, and should, use one long tag for all those words and acronyms.

Ah, it turns out that the Tag Cloud displays no more than 45 tags. It won’t be anywhere near as convenient as I has hoped. Nevertheless, I have tried to clean up tags to make what use I can of the tag cloud.

## Introduction

I am looking into Basilevsky because he did something I didn’t understand: he normalized the rows of the Ac matrix (which I denoted Ar). We discussed that, and we illustrated the computations, in the previous two posts. But we did those computations without having any data. I want to take a closer look, with data.

In contrast to As and Ac, which are eigenvector matrices, his Ar matrix is not. Nevertheless, as I said, his Ar is not without some redeeming value. In fact, all three of the A matrices have the same redeeming value.

I will show, first by direct computation and then by proof, that each of these A matrices is the cross covariance between X data and Z data.
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## happenings — latex

Edits: Feb 2.
removed “a” from codes for bold and strong in HTML; and I just noticed that the LateX for color and for size does not display when you hold the mouse over it.

(This wasn’t the first post I intended to put out after the long layoff, but it’s the one that is ready, so here it is. I’ve got a couple in the works, and I hope that one will be ready for Wednesday.)

This post shows a lot of the HTML and the LaTeX that I use.
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