1,722 research outputs found
Kronecker's canonical form and the QZ algorithm
AbstractThis paper examines the behavior of the QZ algorithm which is to be expected when A−λB is close to a singular pencil. The predicted results are fully confirmed by practical experience of using the QZ algorithm on examples of this kind
On a theorem of Feingold
AbstractWe discuss an extension of a theorem which is apparently due to Feingold. Both the theorem and its extension follow mutatis mutandis from the corresponding material associated with the Bauer-Fike theorem. Feingold made no claims for his result and indeed referred to it as trivial. Although it proves to be rather disappointing, an understanding of the source of its weakness is instructive and leads to related techniques which are of greater value
The Asymptotics of Wilkinson's Iteration: Loss of Cubic Convergence
One of the most widely used methods for eigenvalue computation is the
iteration with Wilkinson's shift: here the shift is the eigenvalue of the
bottom principal minor closest to the corner entry. It has been a
long-standing conjecture that the rate of convergence of the algorithm is
cubic. In contrast, we show that there exist matrices for which the rate of
convergence is strictly quadratic. More precisely, let be the matrix having only two nonzero entries and let
be the set of real, symmetric tridiagonal matrices with the same spectrum
as . There exists a neighborhood of which is
invariant under Wilkinson's shift strategy with the following properties. For
, the sequence of iterates exhibits either strictly
quadratic or strictly cubic convergence to zero of the entry . In
fact, quadratic convergence occurs exactly when . Let be
the union of such quadratically convergent sequences : the set has
Hausdorff dimension 1 and is a union of disjoint arcs meeting at
, where ranges over a Cantor set.Comment: 20 pages, 8 figures. Some passages rewritten for clarit
Comparison of local pole assignment methods
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76770/1/AIAA-20171-818.pd
Spectral Statistics: From Disordered to Chaotic Systems
The relation between disordered and chaotic systems is investigated. It is
obtained by identifying the diffusion operator of the disordered systems with
the Perron-Frobenius operator in the general case. This association enables us
to extend results obtained in the diffusive regime to general chaotic systems.
In particular, the two--point level density correlator and the structure factor
for general chaotic systems are calculated and characterized. The behavior of
the structure factor around the Heisenberg time is quantitatively described in
terms of short periodic orbits.Comment: uuencoded file with 1 eps figure, 4 page
A weakly stable algorithm for general Toeplitz systems
We show that a fast algorithm for the QR factorization of a Toeplitz or
Hankel matrix A is weakly stable in the sense that R^T.R is close to A^T.A.
Thus, when the algorithm is used to solve the semi-normal equations R^T.Rx =
A^Tb, we obtain a weakly stable method for the solution of a nonsingular
Toeplitz or Hankel linear system Ax = b. The algorithm also applies to the
solution of the full-rank Toeplitz or Hankel least squares problem.Comment: 17 pages. An old Technical Report with postscript added. For further
details, see http://wwwmaths.anu.edu.au/~brent/pub/pub143.htm
Approach to ergodicity in quantum wave functions
According to theorems of Shnirelman and followers, in the semiclassical limit
the quantum wavefunctions of classically ergodic systems tend to the
microcanonical density on the energy shell. We here develop a semiclassical
theory that relates the rate of approach to the decay of certain classical
fluctuations. For uniformly hyperbolic systems we find that the variance of the
quantum matrix elements is proportional to the variance of the integral of the
associated classical operator over trajectory segments of length , and
inversely proportional to , where is the Heisenberg
time, being the mean density of states. Since for these systems the
classical variance increases linearly with , the variance of the matrix
elements decays like . For non-hyperbolic systems, like Hamiltonians
with a mixed phase space and the stadium billiard, our results predict a slower
decay due to sticking in marginally unstable regions. Numerical computations
supporting these conclusions are presented for the bakers map and the hydrogen
atom in a magnetic field.Comment: 11 pages postscript and 4 figures in two files, tar-compressed and
uuencoded using uufiles, to appear in Phys Rev E. For related papers, see
http://www.icbm.uni-oldenburg.de/icbm/kosy/ag.htm
Effect of parity on the epidemiologic profile of Malawian women presenting for obstetric fistula repair: A cross sectional study
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