strsen
strsen - reorder the real Schur factorization of a real matrix A = Q*T*Q**T, so that a selected cluster of eigenvalues appears in the leading diagonal blocks of the upper quasi-triangular matrix T,
SUBROUTINE STRSEN( JOB, COMPQ, SELECT, N, T, LDT, Q, LDQ, WR, WI, M,
* S, SEP, WORK, LWORK, IWORK, LIWORK, INFO)
CHARACTER * 1 JOB, COMPQ
INTEGER N, LDT, LDQ, M, LWORK, LIWORK, INFO
INTEGER IWORK(*)
LOGICAL SELECT(*)
REAL S, SEP
REAL T(LDT,*), Q(LDQ,*), WR(*), WI(*), WORK(*)
SUBROUTINE STRSEN_64( JOB, COMPQ, SELECT, N, T, LDT, Q, LDQ, WR, WI,
* M, S, SEP, WORK, LWORK, IWORK, LIWORK, INFO)
CHARACTER * 1 JOB, COMPQ
INTEGER*8 N, LDT, LDQ, M, LWORK, LIWORK, INFO
INTEGER*8 IWORK(*)
LOGICAL*8 SELECT(*)
REAL S, SEP
REAL T(LDT,*), Q(LDQ,*), WR(*), WI(*), WORK(*)
SUBROUTINE TRSEN( JOB, COMPQ, SELECT, N, T, [LDT], Q, [LDQ], WR, WI,
* M, S, SEP, [WORK], [LWORK], [IWORK], [LIWORK], [INFO])
CHARACTER(LEN=1) :: JOB, COMPQ
INTEGER :: N, LDT, LDQ, M, LWORK, LIWORK, INFO
INTEGER, DIMENSION(:) :: IWORK
LOGICAL, DIMENSION(:) :: SELECT
REAL :: S, SEP
REAL, DIMENSION(:) :: WR, WI, WORK
REAL, DIMENSION(:,:) :: T, Q
SUBROUTINE TRSEN_64( JOB, COMPQ, SELECT, N, T, [LDT], Q, [LDQ], WR,
* WI, M, S, SEP, [WORK], [LWORK], [IWORK], [LIWORK], [INFO])
CHARACTER(LEN=1) :: JOB, COMPQ
INTEGER(8) :: N, LDT, LDQ, M, LWORK, LIWORK, INFO
INTEGER(8), DIMENSION(:) :: IWORK
LOGICAL(8), DIMENSION(:) :: SELECT
REAL :: S, SEP
REAL, DIMENSION(:) :: WR, WI, WORK
REAL, DIMENSION(:,:) :: T, Q
#include <sunperf.h>
void strsen(char job, char compq, logical *select, int n, float *t, int ldt, float *q, int ldq, float *wr, float *wi, int *m, float *s, float *sep, int *info);
void strsen_64(char job, char compq, logical *select, long n, float *t, long ldt, float *q, long ldq, float *wr, float *wi, long *m, float *s, float *sep, long *info);
strsen reorders the real Schur factorization of a real matrix
A = Q*T*Q**T, so that a selected cluster of eigenvalues appears in
the leading diagonal blocks of the upper quasi-triangular matrix T,
and the leading columns of Q form an orthonormal basis of the
corresponding right invariant subspace.
Optionally the routine computes the reciprocal condition numbers of
the cluster of eigenvalues and/or the invariant subspace.
T must be in Schur canonical form (as returned by SHSEQR), that is,
block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each
2-by-2 diagonal block has its diagonal elemnts equal and its
off-diagonal elements of opposite sign.
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* JOB (input)
-
Specifies whether condition numbers are required for the
cluster of eigenvalues (S) or the invariant subspace (SEP):
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* COMPQ (input)
-
-
* SELECT (input)
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SELECT specifies the eigenvalues in the selected cluster. To
select a real eigenvalue w(j), SELECT(j) must be set to
.TRUE.. To select a complex conjugate pair of eigenvalues
w(j) and w(j+1), corresponding to a 2-by-2 diagonal block,
either SELECT(j) or SELECT(j+1) or both must be set to
.TRUE.; a complex conjugate pair of eigenvalues must be
either both included in the cluster or both excluded.
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* N (input)
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The order of the matrix T. N >= 0.
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* T (input/output)
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On entry, the upper quasi-triangular matrix T, in Schur
canonical form.
On exit, T is overwritten by the reordered matrix T, again in
Schur canonical form, with the selected eigenvalues in the
leading diagonal blocks.
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* LDT (input)
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The leading dimension of the array T. LDT >= max(1,N).
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* Q (input)
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On entry, if COMPQ = 'V', the matrix Q of Schur vectors.
On exit, if COMPQ = 'V', Q has been postmultiplied by the
orthogonal transformation matrix which reorders T; the
leading M columns of Q form an orthonormal basis for the
specified invariant subspace.
If COMPQ = 'N', Q is not referenced.
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* LDQ (input)
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The leading dimension of the array Q.
LDQ >= 1; and if COMPQ = 'V', LDQ >= N.
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* WR (output)
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The real and imaginary parts, respectively, of the reordered
eigenvalues of T. The eigenvalues are stored in the same
order as on the diagonal of T, with WR(i) = T(i,i) and, if
T(i:i+1,i:i+1) is a 2-by-2 diagonal block, WI(i) > 0 and
WI(i+1) = -WI(i). Note that if a complex eigenvalue is
sufficiently ill-conditioned, then its value may differ
significantly from its value before reordering.
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* WI (output)
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See the description of WR.
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* M (output)
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The dimension of the specified invariant subspace.
0 < = M <= N.
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* S (output)
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If JOB = 'E' or 'B', S is a lower bound on the reciprocal
condition number for the selected cluster of eigenvalues.
S cannot underestimate the true reciprocal condition number
by more than a factor of sqrt(N). If M = 0 or N, S = 1.
If JOB = 'N' or 'V', S is not referenced.
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* SEP (output)
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If JOB = 'V' or 'B', SEP is the estimated reciprocal
condition number of the specified invariant subspace. If
M = 0 or N, SEP = norm(T).
If JOB = 'N' or 'E', SEP is not referenced.
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* WORK (workspace)
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On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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* LWORK (input)
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The dimension of the array WORK.
If JOB = 'N', LWORK >= max(1,N);
if JOB = 'E', LWORK >= M*(N-M);
if JOB = 'V' or 'B', LWORK >= 2*M*(N-M).
If LWORK = -1, then a workspace query is assumed; the routine
only calculates the optimal size of the WORK array, returns
this value as the first entry of the WORK array, and no error
message related to LWORK is issued by XERBLA.
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* IWORK (workspace)
-
If JOB = 'N' or 'E', IWORK is not referenced.
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* LIWORK (input)
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The dimension of the array IWORK.
If JOB = 'N' or 'E', LIWORK >= 1;
if JOB = 'V' or 'B', LIWORK >= M*(N-M).
If LIWORK = -1, then a workspace query is assumed; the
routine only calculates the optimal size of the IWORK array,
returns this value as the first entry of the IWORK array, and
no error message related to LIWORK is issued by XERBLA.
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* INFO (output)
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