• NAME
• SYNOPSIS
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

dsyev - compute all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A

SYNOPSIS

  SUBROUTINE DSYEV( JOBZ, UPLO, N, A, LDA, W, WORK, LDWORK, INFO)
  CHARACTER * 1 JOBZ, UPLO
  INTEGER N, LDA, LDWORK, INFO
  DOUBLE PRECISION A(LDA,*), W(*), WORK(*)

  SUBROUTINE DSYEV_64( JOBZ, UPLO, N, A, LDA, W, WORK, LDWORK, INFO)
  CHARACTER * 1 JOBZ, UPLO
  INTEGER*8 N, LDA, LDWORK, INFO
  DOUBLE PRECISION A(LDA,*), W(*), WORK(*)

F95 INTERFACE

  SUBROUTINE SYEV( JOBZ, UPLO, [N], A, [LDA], W, [WORK], [LDWORK], 
 *       [INFO])
  CHARACTER(LEN=1) :: JOBZ, UPLO
  INTEGER :: N, LDA, LDWORK, INFO
  REAL(8), DIMENSION(:) :: W, WORK
  REAL(8), DIMENSION(:,:) :: A

  SUBROUTINE SYEV_64( JOBZ, UPLO, [N], A, [LDA], W, [WORK], [LDWORK], 
 *       [INFO])
  CHARACTER(LEN=1) :: JOBZ, UPLO
  INTEGER(8) :: N, LDA, LDWORK, INFO
  REAL(8), DIMENSION(:) :: W, WORK
  REAL(8), DIMENSION(:,:) :: A

C INTERFACE

#include <sunperf.h>

void dsyev(char jobz, char uplo, int n, double *a, int lda, double *w, int *info);

void dsyev_64(char jobz, char uplo, long n, double *a, long lda, double *w, long *info);

PURPOSE

dsyev computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A.

ARGUMENTS

• JOBZ (input)
  

   = 'N':  Compute eigenvalues only;

   = 'V':  Compute eigenvalues and eigenvectors.

• UPLO (input)
  

   = 'U':  Upper triangle of A is stored;

   = 'L':  Lower triangle of A is stored.

• N (input)
  The order of the matrix A. N > = 0.

• A (input/output)
  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. If UPLO = 'L', the leading N-by-N lower triangular part of A contains the lower triangular part of the matrix A. On exit, if JOBZ = 'V', then if INFO = 0, A contains the orthonormal eigenvectors of the matrix A. If JOBZ = 'N', then on exit the lower triangle (if UPLO ='L') or the upper triangle (if UPLO ='U') of A, including the diagonal, is destroyed.

• LDA (input)
  The leading dimension of the array A. LDA > = max(1,N).

• W (output)
  If INFO = 0, the eigenvalues in ascending order.

• WORK (workspace)
  On exit, if INFO = 0, WORK(1) returns the optimal LDWORK.

• LDWORK (input)
  The length of the array WORK. LDWORK > = max(1,3*N-1). For optimal efficiency, LDWORK > = (NB+2)*N, where NB is the blocksize for SSYTRD returned by ILAENV.

  If LDWORK = -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 LDWORK is issued by XERBLA.

• INFO (output)
  

   = 0:  successful exit

   < 0:  if INFO  = -i, the i-th argument had an illegal value

   > 0:  if INFO  = i, the algorithm failed to converge; i
  off-diagonal elements of an intermediate tridiagonal
  form did not converge to zero.