SUBROUTINE DSPEVD( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, LWORK, IWORK, * LIWORK, INFO) CHARACTER * 1 JOBZ, UPLO INTEGER N, LDZ, LWORK, LIWORK, INFO INTEGER IWORK(*) DOUBLE PRECISION AP(*), W(*), Z(LDZ,*), WORK(*) SUBROUTINE DSPEVD_64( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, LWORK, * IWORK, LIWORK, INFO) CHARACTER * 1 JOBZ, UPLO INTEGER*8 N, LDZ, LWORK, LIWORK, INFO INTEGER*8 IWORK(*) DOUBLE PRECISION AP(*), W(*), Z(LDZ,*), WORK(*)
SUBROUTINE SPEVD( JOBZ, UPLO, [N], AP, W, Z, [LDZ], [WORK], [LWORK], * [IWORK], [LIWORK], [INFO]) CHARACTER(LEN=1) :: JOBZ, UPLO INTEGER :: N, LDZ, LWORK, LIWORK, INFO INTEGER, DIMENSION(:) :: IWORK REAL(8), DIMENSION(:) :: AP, W, WORK REAL(8), DIMENSION(:,:) :: Z SUBROUTINE SPEVD_64( JOBZ, UPLO, [N], AP, W, Z, [LDZ], [WORK], * [LWORK], [IWORK], [LIWORK], [INFO]) CHARACTER(LEN=1) :: JOBZ, UPLO INTEGER(8) :: N, LDZ, LWORK, LIWORK, INFO INTEGER(8), DIMENSION(:) :: IWORK REAL(8), DIMENSION(:) :: AP, W, WORK REAL(8), DIMENSION(:,:) :: Z
void dspevd(char jobz, char uplo, int n, double *ap, double *w, double *z, int ldz, int *info);
void dspevd_64(char jobz, char uplo, long n, double *ap, double *w, double *z, long ldz, long *info);
The divide and conquer algorithm 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.
On exit, AP is overwritten by values generated during the reduction to tridiagonal form. If UPLO = 'U', the diagonal and first superdiagonal of the tridiagonal matrix T overwrite the corresponding elements of A, and if UPLO = 'L', the diagonal and first subdiagonal of T overwrite the corresponding elements of A.
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.
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.