sstedc
sstedc - compute all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the divide and conquer method
SUBROUTINE SSTEDC( COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK,
* LIWORK, INFO)
CHARACTER * 1 COMPZ
INTEGER N, LDZ, LWORK, LIWORK, INFO
INTEGER IWORK(*)
REAL D(*), E(*), Z(LDZ,*), WORK(*)
SUBROUTINE SSTEDC_64( COMPZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK,
* LIWORK, INFO)
CHARACTER * 1 COMPZ
INTEGER*8 N, LDZ, LWORK, LIWORK, INFO
INTEGER*8 IWORK(*)
REAL D(*), E(*), Z(LDZ,*), WORK(*)
SUBROUTINE STEDC( COMPZ, N, D, E, Z, [LDZ], [WORK], [LWORK], [IWORK],
* [LIWORK], [INFO])
CHARACTER(LEN=1) :: COMPZ
INTEGER :: N, LDZ, LWORK, LIWORK, INFO
INTEGER, DIMENSION(:) :: IWORK
REAL, DIMENSION(:) :: D, E, WORK
REAL, DIMENSION(:,:) :: Z
SUBROUTINE STEDC_64( COMPZ, N, D, E, Z, [LDZ], [WORK], [LWORK],
* [IWORK], [LIWORK], [INFO])
CHARACTER(LEN=1) :: COMPZ
INTEGER(8) :: N, LDZ, LWORK, LIWORK, INFO
INTEGER(8), DIMENSION(:) :: IWORK
REAL, DIMENSION(:) :: D, E, WORK
REAL, DIMENSION(:,:) :: Z
#include <sunperf.h>
void sstedc(char compz, int n, float *d, float *e, float *z, int ldz, int *info);
void sstedc_64(char compz, long n, float *d, float *e, float *z, long ldz, long *info);
sstedc computes all eigenvalues and, optionally, eigenvectors of a
symmetric tridiagonal matrix using the divide and conquer method.
The eigenvectors of a full or band real symmetric matrix can also be
found if SSYTRD or SSPTRD or SSBTRD has been used to reduce this
matrix to tridiagonal form.
This code makes very mild assumptions about floating point
arithmetic. It will work on machines with a guard digit in
add/subtract, or on those binary machines without guard digits
which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or Cray-2.
It could conceivably fail on hexadecimal or decimal machines
without guard digits, but we know of none. See SLAED3 for details.
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* COMPZ (input)
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* N (input)
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The dimension of the symmetric tridiagonal matrix. N >= 0.
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* D (input/output)
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On entry, the diagonal elements of the tridiagonal matrix.
On exit, if INFO = 0, the eigenvalues in ascending order.
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* E (input/output)
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On entry, the subdiagonal elements of the tridiagonal matrix.
On exit, E has been destroyed.
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* Z (input)
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On entry, if COMPZ = 'V', then Z contains the orthogonal
matrix used in the reduction to tridiagonal form.
On exit, if INFO = 0, then if COMPZ = 'V', Z contains the
orthonormal eigenvectors of the original symmetric matrix,
and if COMPZ = 'I', Z contains the orthonormal eigenvectors
of the symmetric tridiagonal matrix.
If COMPZ = 'N', then Z is not referenced.
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* LDZ (input)
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The leading dimension of the array Z. LDZ >= 1.
If eigenvectors are desired, then LDZ >= max(1,N).
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* WORK (workspace)
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dimension (LWORK)
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 COMPZ = 'N' or N <= 1 then LWORK must be at least 1.
If COMPZ = 'V' and N > 1 then LWORK must be at least
( 1 + 3*N + 2*N*lg N + 3*N**2 ),
where lg( N ) = smallest integer k such
that 2**k >= N.
If COMPZ = 'I' and N > 1 then LWORK must be at least
( 1 + 4*N + N**2 ).
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)
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On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
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* LIWORK (input)
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The dimension of the array IWORK.
If COMPZ = 'N' or N <= 1 then LIWORK must be at least 1.
If COMPZ = 'V' and N > 1 then LIWORK must be at least
( 6 + 6*N + 5*N*lg N ).
If COMPZ = 'I' and N > 1 then LIWORK must be at least
( 3 + 5*N ).
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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