213 research outputs found
Quasiseparable Hessenberg reduction of real diagonal plus low rank matrices and applications
We present a novel algorithm to perform the Hessenberg reduction of an
matrix of the form where is diagonal with
real entries and and are matrices with . The
algorithm has a cost of arithmetic operations and is based on the
quasiseparable matrix technology. Applications are shown to solving polynomial
eigenvalue problems and some numerical experiments are reported in order to
analyze the stability of the approac
Multilevel quasiseparable matrices in PDE-constrained optimization
Optimization problems with constraints in the form of a partial differential
equation arise frequently in the process of engineering design. The
discretization of PDE-constrained optimization problems results in large-scale
linear systems of saddle-point type. In this paper we propose and develop a
novel approach to solving such systems by exploiting so-called quasiseparable
matrices. One may think of a usual quasiseparable matrix as of a discrete
analog of the Green's function of a one-dimensional differential operator. Nice
feature of such matrices is that almost every algorithm which employs them has
linear complexity. We extend the application of quasiseparable matrices to
problems in higher dimensions. Namely, we construct a class of preconditioners
which can be computed and applied at a linear computational cost. Their use
with appropriate Krylov methods leads to algorithms of nearly linear
complexity
Groups of banded matrices with banded inverses
A product A=F[subscript 1]...F[subscript N] of invertible block-diagonal matrices will be banded with a banded
inverse. We establish this factorization with the number N controlled by the bandwidths w
and not by the matrix size n. When A is an orthogonal matrix, or a permutation, or banded
plus finite rank, the factors F[subscript i] have w=1 and generate that corresponding group. In the
case of infinite matrices, conjectures remain open
A Parallel Hierarchical Blocked Adaptive Cross Approximation Algorithm
This paper presents a hierarchical low-rank decomposition algorithm assuming
any matrix element can be computed in time. The proposed algorithm
computes rank-revealing decompositions of sub-matrices with a blocked adaptive
cross approximation (BACA) algorithm, followed by a hierarchical merge
operation via truncated singular value decompositions (H-BACA). The proposed
algorithm significantly improves the convergence of the baseline ACA algorithm
and achieves reduced computational complexity compared to the full
decompositions such as rank-revealing QR decompositions. Numerical results
demonstrate the efficiency, accuracy and parallel efficiency of the proposed
algorithm
The Main Diagonal of a Permutation Matrix
By counting 1's in the "right half" of consecutive rows, we locate the
main diagonal of any doubly infinite permutation matrix with bandwidth .
Then the matrix can be correctly centered and factored into block-diagonal
permutation matrices. Part II of the paper discusses the same questions for the
much larger class of band-dominated matrices. The main diagonal is determined
by the Fredholm index of a singly infinite submatrix. Thus the main diagonal is
determined "at infinity" in general, but from only rows for banded
permutations
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