MATLAB Function Reference |
Syntax
Description
H = hess(A)
finds H
, the Hessenberg form of matrix A
.
[P,H] = hess(A)
produces a Hessenberg matrix H
and a unitary matrix P
so that A
=
P*H*P'
and P'*P
= eye(size(A))
.
[AA,BB,Q,Z] = HESS(A,B)
for square matrices A
and B
, produces an upper Hessenberg matrix AA
, an upper triangular matrix BB
, and unitary matrices Q
and Z
such that Q*A*Z = AA
and Q*B*Z = BB
.
Definition
A Hessenberg matrix is zero below the first subdiagonal. If the matrix is symmetric or Hermitian, the form is tridiagonal. This matrix has the same eigenvalues as the original, but less computation is needed to reveal them.
Examples
H
is a 3-by-3 eigenvalue test matrix:
Its Hessenberg form introduces a single zero in the (3,1) position:
Inputs of Type Double
For inputs of type double, hess
uses the following LAPACK routines to compute the Hessenberg form of a matrix:
Inputs of Type Single
For inputs of type single
, hess
uses the following LAPACK routines to compute the Hessenberg form of a matrix:
See Also
References
[1] Anderson, E., Z. Bai, C. Bischof, S. Blackford, J. Demmel, J. Dongarra, J. Du Croz, A. Greenbaum, S. Hammarling, A. McKenney, and D. Sorensen, LAPACK User's Guide (http://www.netlib.org/lapack/lug/ lapack_lug.html), Third Edition, SIAM, Philadelphia, 1999.
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