dsytrd
dsytrd - reduce a real symmetric matrix A to real symmetric tridiagonal form T by an orthogonal similarity transformation
SUBROUTINE DSYTRD( UPLO, N, A, LDA, D, E, TAU, WORK, LWORK, INFO)
CHARACTER * 1 UPLO
INTEGER N, LDA, LWORK, INFO
DOUBLE PRECISION A(LDA,*), D(*), E(*), TAU(*), WORK(*)
SUBROUTINE DSYTRD_64( UPLO, N, A, LDA, D, E, TAU, WORK, LWORK, INFO)
CHARACTER * 1 UPLO
INTEGER*8 N, LDA, LWORK, INFO
DOUBLE PRECISION A(LDA,*), D(*), E(*), TAU(*), WORK(*)
SUBROUTINE SYTRD( UPLO, N, A, [LDA], D, E, TAU, [WORK], [LWORK],
* [INFO])
CHARACTER(LEN=1) :: UPLO
INTEGER :: N, LDA, LWORK, INFO
REAL(8), DIMENSION(:) :: D, E, TAU, WORK
REAL(8), DIMENSION(:,:) :: A
SUBROUTINE SYTRD_64( UPLO, N, A, [LDA], D, E, TAU, [WORK], [LWORK],
* [INFO])
CHARACTER(LEN=1) :: UPLO
INTEGER(8) :: N, LDA, LWORK, INFO
REAL(8), DIMENSION(:) :: D, E, TAU, WORK
REAL(8), DIMENSION(:,:) :: A
#include <sunperf.h>
void dsytrd(char uplo, int n, double *a, int lda, double *d, double *e, double *tau, int *info);
void dsytrd_64(char uplo, long n, double *a, long lda, double *d, double *e, double *tau, long *info);
dsytrd reduces a real symmetric matrix A to real symmetric
tridiagonal form T by an orthogonal similarity transformation:
Q**T * A * Q = T.
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* UPLO (input)
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* N (input)
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The order of the matrix A. N >= 0.
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* A (input)
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On entry, the symmetric matrix A. If UPLO = 'U', the leading
N-by-N upper triangular part of A contains the upper
triangular part of the matrix A, and the strictly lower
triangular part of A is not referenced. If UPLO = 'L', the
leading N-by-N lower triangular part of A contains the lower
triangular part of the matrix A, and the strictly upper
triangular part of A is not referenced.
On exit, if UPLO = 'U', the diagonal and first superdiagonal
of A are overwritten by the corresponding elements of the
tridiagonal matrix T, and the elements above the first
superdiagonal, with the array TAU, represent the orthogonal
matrix Q as a product of elementary reflectors; if UPLO
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* LDA (input)
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The leading dimension of the array A. LDA >= max(1,N).
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* D (output)
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The diagonal elements of the tridiagonal matrix T:
D(i) = A(i,i).
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* E (output)
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The off-diagonal elements of the tridiagonal matrix T:
E(i) = A(i,i+1) if UPLO = 'U', E(i) = A(i+1,i) if UPLO = 'L'.
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* TAU (output)
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The scalar factors of the elementary reflectors (see Further
Details).
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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. LWORK >= 1.
For optimum performance LWORK >= N*NB, where NB is the
optimal blocksize.
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)
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