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- Newsgroups: sci.math
- Path: sparky!uunet!munnari.oz.au!manuel!rsphy1.anu.edu.au!rwc124
- From: rwc124@rsphy1.anu.edu.au (Roderick Vance)
- Subject: Unitary Matrix Goups
- Message-ID: <1992Sep2.034701.10049@newshost.anu.edu.au>
- Sender: news@newshost.anu.edu.au
- Reply-To: rwc124@rsphy1.anu.edu.au (Roderick Vance)
- Organization: Optical Sciences Centre, Australian National University
- Date: Wed, 2 Sep 92 03:47:01 GMT
- Lines: 43
-
- Keywor
-
- My question is about the group, (call it U) of all NxN unitary matrices (N a
- constant for a given discussion) and on the structure of subgroups
- generated by a restricted set of matrices.
-
- To illustrate with a concrete example, consider the set T of all tridiagonal,
- symmetric matrices. Form from them the set of unitary matrices:
-
- T1 = {exp(i H), H belongs to T}
-
- and then find the smallest subgroup (call it U1) of U containing T1. I
- should like to find
- out the following things about U1:
-
- Is U1 all of U?
-
- If not, can one come up with a simple test of whether or not a matrix
- belongs to U1 ?
-
- What bits of group/matrix theory should i be reading about to try to
- solve these problems?
-
- I realise that i may face an horrendously complex task. Even if you
- consider an
- innocent looking animal such as the smallest subgroup of U containing
- two unitary matrices
- A and B, where A and B do not commute, then it seems to me that, for
- pathological choices
- of A and B, you might wind up with something as complex as the free
- group generated by
- {A,B}. In general, there would seem to be no way of reducing arbitrary
- products A^r1*B^r2*...
- A^rn*B^rn, {r1..rn are integers}. I am probably wrong about this last
- conjecture since i know
- next to nichts about this subject.
-
-
- Many thanks in advance
-
- Rod Vance
- Optical Sciences Centre
- Australian National University
-