Purpose
To move the eigenvalues with strictly negative real parts of an
N-by-N real skew-Hamiltonian/Hamiltonian pencil aS - bH in
structured Schur form,
( A D ) ( B F )
S = ( ), H = ( ),
( 0 A' ) ( 0 -B' )
with A upper triangular and B upper quasi-triangular, to the
leading principal subpencil, while keeping the triangular form:
( Aout Dout ) ( Bout Fout )
Sout = ( ), Hout = ( ), where
( 0 Aout' ) ( 0 -Bout' )
Aout is upper triangular and Bout is upper quasi-triangular.
Optionally, if COMPQ = 'I' or COMPQ = 'U', an orthogonal matrix Q
is determined such that the pencil
( 0 I )
J Q' J' (aS - bH) Q = aSout - bHout, with J = ( ),
( -I 0 )
keeps the triangular form, but all eigenvalues with strictly
negative real part are in the leading principal subpencil.
Specification
SUBROUTINE MB03JD( COMPQ, N, A, LDA, D, LDD, B, LDB, F, LDF, Q,
$ LDQ, NEIG, IWORK, LIWORK, DWORK, LDWORK, INFO )
C .. Scalar Arguments ..
CHARACTER COMPQ
INTEGER INFO, LDA, LDB, LDD, LDF, LDQ, LDWORK, LIWORK,
$ N, NEIG
C .. Array Arguments ..
INTEGER IWORK( * )
DOUBLE PRECISION A( LDA, * ), B( LDB, * ), D( LDD, * ),
$ DWORK( * ), F( LDF, * ), Q( LDQ, * )
Arguments
Mode Parameters
COMPQ CHARACTER*1
Specifies whether or not the orthogonal transformations
should be accumulated in the array Q, as follows:
= 'N': Q is not computed;
= 'I': the array Q is initialized internally to the unit
matrix, and the orthogonal matrix Q is returned;
= 'U': the array Q contains an orthogonal matrix Q0 on
entry, and the matrix Q0*Q is returned, where Q
is the product of the orthogonal transformations
that are applied to the pencil aS - bH to reorder
the eigenvalues.
Input/Output Parameters
N (input) INTEGER
The order of the pencil aS - bH. N >= 0, even.
A (input/output) DOUBLE PRECISION array, dimension
(LDA, N/2)
On entry, the leading N/2-by-N/2 part of this array must
contain the upper triangular matrix A. The elements of the
strictly lower triangular part of this array are not used.
On exit, the leading N/2-by-N/2 part of this array
contains the transformed matrix Aout.
LDA INTEGER
The leading dimension of the array A. LDA >= MAX(1, N/2).
D (input/output) DOUBLE PRECISION array, dimension
(LDD, N/2)
On entry, the leading N/2-by-N/2 part of this array must
contain the upper triangular part of the skew-symmetric
matrix D. The diagonal need not be set to zero.
On exit, the leading N/2-by-N/2 part of this array
contains the transformed upper triangular part of the
matrix Dout.
The strictly lower triangular part of this array is
not referenced, except for the element D(N/2,N/2-1), but
its initial value is preserved.
LDD INTEGER
The leading dimension of the array D. LDD >= MAX(1, N/2).
B (input/output) DOUBLE PRECISION array, dimension
(LDB, N/2)
On entry, the leading N/2-by-N/2 part of this array must
contain the upper quasi-triangular matrix B.
On exit, the leading N/2-by-N/2 part of this array
contains the transformed upper quasi-triangular part of
the matrix Bout.
The part below the first subdiagonal of this array is
not referenced.
LDB INTEGER
The leading dimension of the array B. LDB >= MAX(1, N/2).
F (input/output) DOUBLE PRECISION array, dimension
(LDF, N/2)
On entry, the leading N/2-by-N/2 part of this array must
contain the upper triangular part of the symmetric matrix
F.
On exit, the leading N/2-by-N/2 part of this array
contains the transformed upper triangular part of the
matrix Fout.
The strictly lower triangular part of this array is not
referenced, except for the element F(N/2,N/2-1), but its
initial value is preserved.
LDF INTEGER
The leading dimension of the array F. LDF >= MAX(1, N/2).
Q (input/output) DOUBLE PRECISION array, dimension (LDQ, N)
On entry, if COMPQ = 'U', then the leading N-by-N part of
this array must contain a given matrix Q0, and on exit,
the leading N-by-N part of this array contains the product
of the input matrix Q0 and the transformation matrix Q
used to transform the matrices S and H.
On exit, if COMPQ = 'I', then the leading N-by-N part of
this array contains the orthogonal transformation matrix
Q.
If COMPQ = 'N' this array is not referenced.
LDQ INTEGER
The leading dimension of of the array Q.
LDQ >= 1, if COMPQ = 'N';
LDQ >= MAX(1, N), if COMPQ = 'I' or COMPQ = 'U'.
NEIG (output) INTEGER
The number of eigenvalues in aS - bH with strictly
negative real part.
Workspace
IWORK INTEGER array, dimension (LIWORK)
LIWORK INTEGER
The dimension of the array IWORK.
LIWORK >= N+1.
DWORK DOUBLE PRECISION array, dimension (LDWORK)
LDWORK INTEGER
The dimension of the array DWORK.
If COMPQ = 'N',
LDWORK >= MAX(2*N+32,108);
if COMPQ = 'I' or COMPQ = 'U',
LDWORK >= MAX(4*N+32,108).
Error Indicator
INFO INTEGER
= 0: succesful exit;
< 0: if INFO = -i, the i-th argument had an illegal value;
= 1: error occured during execution of MB03DD;
= 2: error occured during execution of MB03HD.
Method
The algorithm reorders the eigenvalues like the following scheme:
Step 1: Reorder the eigenvalues in the subpencil aA - bB.
I. Reorder the eigenvalues with negative real parts to the
top.
II. Reorder the eigenvalues with positive real parts to the
bottom.
Step 2: Reorder the remaining eigenvalues with negative real
parts in the pencil aS - bH.
I. Exchange the eigenvalues between the last diagonal block
in aA - bB and the last diagonal block in aS - bH.
II. Move the eigenvalues of the R-th block to the (MM+1)-th
block, where R denotes the number of upper quasi-
triangular blocks in aA - bB and MM denotes the current
number of blocks in aA - bB with eigenvalues with negative
real parts.
The algorithm uses a sequence of orthogonal transformations as
described on page 33 in [1]. To achieve those transformations the
elementary subroutines MB03DD and MB03HD are called for the
corresponding matrix structures.
References
[1] Benner, P., Byers, R., Losse, P., Mehrmann, V. and Xu, H.
Numerical Solution of Real Skew-Hamiltonian/Hamiltonian
Eigenproblems.
Tech. Rep., Technical University Chemnitz, Germany,
Nov. 2007.
Numerical Aspects
3 The algorithm is numerically backward stable and needs O(N ) real floating point operations.Further Comments
NoneExample
Program Text
NoneProgram Data
NoneProgram Results
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