stgexc
stgexc - reorder the generalized real Schur decomposition of a real matrix pair (A,B) using an orthogonal equivalence transformation (A, B) = Q * (A, B) * Z',
SUBROUTINE STGEXC( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z, LDZ,
* IFST, ILST, WORK, LWORK, INFO)
INTEGER N, LDA, LDB, LDQ, LDZ, IFST, ILST, LWORK, INFO
LOGICAL WANTQ, WANTZ
REAL A(LDA,*), B(LDB,*), Q(LDQ,*), Z(LDZ,*), WORK(*)
SUBROUTINE STGEXC_64( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
* LDZ, IFST, ILST, WORK, LWORK, INFO)
INTEGER*8 N, LDA, LDB, LDQ, LDZ, IFST, ILST, LWORK, INFO
LOGICAL*8 WANTQ, WANTZ
REAL A(LDA,*), B(LDB,*), Q(LDQ,*), Z(LDZ,*), WORK(*)
SUBROUTINE TGEXC( WANTQ, WANTZ, N, A, [LDA], B, [LDB], Q, [LDQ], Z,
* [LDZ], IFST, ILST, [WORK], [LWORK], [INFO])
INTEGER :: N, LDA, LDB, LDQ, LDZ, IFST, ILST, LWORK, INFO
LOGICAL :: WANTQ, WANTZ
REAL, DIMENSION(:) :: WORK
REAL, DIMENSION(:,:) :: A, B, Q, Z
SUBROUTINE TGEXC_64( WANTQ, WANTZ, N, A, [LDA], B, [LDB], Q, [LDQ],
* Z, [LDZ], IFST, ILST, [WORK], [LWORK], [INFO])
INTEGER(8) :: N, LDA, LDB, LDQ, LDZ, IFST, ILST, LWORK, INFO
LOGICAL(8) :: WANTQ, WANTZ
REAL, DIMENSION(:) :: WORK
REAL, DIMENSION(:,:) :: A, B, Q, Z
#include <sunperf.h>
void stgexc(logical wantq, logical wantz, int n, float *a, int lda, float *b, int ldb, float *q, int ldq, float *z, int ldz, int *ifst, int *ilst, int *info);
void stgexc_64(logical wantq, logical wantz, long n, float *a, long lda, float *b, long ldb, float *q, long ldq, float *z, long ldz, long *ifst, long *ilst, long *info);
stgexc reorders the generalized real Schur decomposition of a real
matrix pair (A,B) using an orthogonal equivalence transformation
so that the diagonal block of (A, B) with row index IFST is moved
to row ILST.
(A, B) must be in generalized real Schur canonical form (as returned
by SGGES), i.e. A is block upper triangular with 1-by-1 and 2-by-2
diagonal blocks. B is upper triangular.
Optionally, the matrices Q and Z of generalized Schur vectors are
updated.
Q(in) * A(in) * Z(in)' = Q(out) * A(out) * Z(out)'
Q(in) * B(in) * Z(in)' = Q(out) * B(out) * Z(out)'
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* WANTQ (input)
-
.TRUE. : update the left transformation matrix Q;
.FALSE.: do not update Q.
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* WANTZ (input)
-
.TRUE. : update the right transformation matrix Z;
.FALSE.: do not update Z.
-
* N (input)
-
The order of the matrices A and B. N >= 0.
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* A (input/output)
-
On entry, the matrix A in generalized real Schur canonical
form.
On exit, the updated matrix A, again in generalized
real Schur canonical form.
-
* LDA (input)
-
The leading dimension of the array A. LDA >= max(1,N).
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* B (input/output)
-
On entry, the matrix B in generalized real Schur canonical
form (A,B).
On exit, the updated matrix B, again in generalized
real Schur canonical form (A,B).
-
* LDB (input)
-
The leading dimension of the array B. LDB >= max(1,N).
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* Q (input/output)
-
On entry, if WANTQ = .TRUE., the orthogonal matrix Q.
On exit, the updated matrix Q.
If WANTQ = .FALSE., Q is not referenced.
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* LDQ (input)
-
The leading dimension of the array Q. LDQ >= 1.
If WANTQ = .TRUE., LDQ >= N.
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* Z (input/output)
-
On entry, if WANTZ = .TRUE., the orthogonal matrix Z.
On exit, the updated matrix Z.
If WANTZ = .FALSE., Z is not referenced.
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* LDZ (input)
-
The leading dimension of the array Z. LDZ >= 1.
If WANTZ = .TRUE., LDZ >= N.
-
* IFST (input/output)
-
Specify the reordering of the diagonal blocks of (A, B).
The block with row index IFST is moved to row ILST, by a
sequence of swapping between adjacent blocks.
On exit, if IFST pointed on entry to the second row of
a 2-by-2 block, it is changed to point to the first row;
ILST always points to the first row of the block in its
final position (which may differ from its input value by
+1 or -1). 1 <= IFST, ILST <= N.
-
* ILST (input/output)
-
See the description of IFST.
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* WORK (workspace)
-
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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* LWORK (input)
-
The dimension of the array WORK. LWORK >= 4*N + 16.
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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* INFO (output)
-