Re: The cosine of a matrix


Gottfried Helms wrote:
Am 24.10.2006 16:33 schrieb schoenfeld.one@xxxxxxxxx:

... nice treatise. What I always was looking for, was
to find an application of that. The only use I ever had
for this was to create commuting matrices, where
C = cos(A) and S=sin(A)
and to use this to demonstrate some examples concerning
commutativity and cos/sin-laws on matrices wih numerical
examples.
Does the mat-cosine/-sine occur anywhere in a
relevant area?

Well, you could say that exp(itH) = cos(tH) + i sin(tH), and
the unitary group generated by a Hermitian matrix
(or self-adjoint operator) occurs all the time...

Robert Israel israel@xxxxxxxxxxx
Department of Mathematics http://www.math.ubc.ca/~israel
University of British Columbia Vancouver, BC, Canada

.