## Self-similar matrices? [closed]

Does anyone know anything about self-similar (infinite) matrices, with more or less fractal(-like) structure and admitting meaningful matrix-algebra operations?

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Also, could the moderators or/and high-reputation users kindly add here a tag "fractals" or something like that? – Igor Korepanov Jan 4 2010 at 12:45
How are they "self-similar" or "fractal"? What Hilbert space are these operators acting on? – John Mangual Jan 4 2010 at 12:47
Well, John, give me some time to think how to explain this... Or, in the case if you can read some Russian, here are two short texts with examples of such matrices: csc.ac.ru/ej/file/4381 and csc.ac.ru/ej/file/4641 . And thanks to Dmitri for creating the fractals tag! – Igor Korepanov Jan 4 2010 at 13:29
This question should be closed, I think. If you can turn it into something more concrete with maybe a motivation and a small explanation, then I would be quite interested in reading it! As it stands, the answer is probably yes, as apparently someone knows something about that kind of matrices. – Mariano Suárez-Alvarez Jan 4 2010 at 19:22
"nobody could say anything" perhaps because the question was too vague? Maybe they even had some information you're looking for, but they had no way to know it! – Reid Barton Jan 5 2010 at 22:41

## closed as not a real question by Mariano Suárez-Alvarez, Reid Barton, Anton Geraschenko♦♦Jan 5 2010 at 23:23

You should learn about the hyperfinite II_1 factor, which is the limit of the inclusions

M_1 --> M_2 --> M_4 --> M_8 --> ....


(here M_k is the k by k matrices over $\mathbb{C}$) where each inclusion is given by tensoring with the identity matrix in M_2. Every 'finite' element is "self-similar" in a sense.

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For the record, btw, I'm in the camp that thinks this is a poor question: too vague, and it's unclear what you mean by "self-similar". Moreover, not knowing whether this answer is basic stuff you already know, or somewthing new, I have little motivation to expand on it. – Scott Morrison Jan 5 2010 at 22:28
Scott, thanks for you answer. I am just studying what this mathoverflow is, and your answer is helpful for this. Perhaps I will explain in the next version of my question that just tensor products are not "fractal enough" - or, otherwise, I may decide that this was a wrong site to ask serious questions. But thank you anyhow! – Igor Korepanov Jan 5 2010 at 22:37
Igor, this is "the wrong site" to ask questions that are so vague that it's not clear what an answer would even look like! In a comment above you equate creativity with vagueness, but I don't see how creativity prevents you from defining the terms that you use in the question. – HW Jan 5 2010 at 23:06
Igor, "anything vaguely resembling self-similarity would work" Except that Scott's answer vaguely resembles self-similarity, and apparently it doesn't work! You could have saved Scott the trouble of giving an answer you didn't need if you'd given more details in the question. – HW Jan 5 2010 at 23:26
Actually, mostly no --- I saw the high noise/signal discussion going on on meta, and gave an answer in order to more clearly highlight the fact that your question was too vague to receive a useful answer. :-) – Scott Morrison Jan 6 2010 at 9:09