LAPACK

NAME¶

stevd - stevd: eig, divide and conquer

SYNOPSIS¶

Functions¶

subroutine dstevd (jobz, n, d, e, z, ldz, work, lwork, iwork, liwork, info)
DSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices subroutine sstevd (jobz, n, d, e, z, ldz, work, lwork, iwork, liwork, info)
SSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

Detailed Description¶

Function Documentation¶

subroutine dstevd (character jobz, integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer lwork, integer, dimension( * ) iwork, integer liwork, integer info)¶

DSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

Purpose:

!>
!> DSTEVD computes all eigenvalues and, optionally, eigenvectors of a
!> real symmetric tridiagonal matrix. If eigenvectors are desired, it
!> uses a divide and conquer algorithm.
!>
!>

Parameters

JOBZ

!>          JOBZ is CHARACTER*1
!>          = 'N':  Compute eigenvalues only;
!>          = 'V':  Compute eigenvalues and eigenvectors.
!>

!>          N is INTEGER
!>          The order of the matrix.  N >= 0.
!>

!>          D is DOUBLE PRECISION array, dimension (N)
!>          On entry, the n diagonal elements of the tridiagonal matrix
!>          A.
!>          On exit, if INFO = 0, the eigenvalues in ascending order.
!>

!>          E is DOUBLE PRECISION array, dimension (N-1)
!>          On entry, the (n-1) subdiagonal elements of the tridiagonal
!>          matrix A, stored in elements 1 to N-1 of E.
!>          On exit, the contents of E are destroyed.
!>

!>          Z is DOUBLE PRECISION array, dimension (LDZ, N)
!>          If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
!>          eigenvectors of the matrix A, with the i-th column of Z
!>          holding the eigenvector associated with D(i).
!>          If JOBZ = 'N', then Z is not referenced.
!>

LDZ

!>          LDZ is INTEGER
!>          The leading dimension of the array Z.  LDZ >= 1, and if
!>          JOBZ = 'V', LDZ >= max(1,N).
!>

WORK

!>          WORK is DOUBLE PRECISION array,
!>                                         dimension (LWORK)
!>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
!>

LWORK

!>          LWORK is INTEGER
!>          The dimension of the array WORK.
!>          If JOBZ  = 'N' or N <= 1 then LWORK must be at least 1.
!>          If JOBZ  = 'V' 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 sizes of the WORK and IWORK
!>          arrays, returns these values as the first entries of the WORK
!>          and IWORK arrays, and no error message related to LWORK or
!>          LIWORK is issued by XERBLA.
!>

IWORK

!>          IWORK is INTEGER array, dimension (MAX(1,LIWORK))
!>          On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
!>

LIWORK

!>          LIWORK is INTEGER
!>          The dimension of the array IWORK.
!>          If JOBZ  = 'N' or N <= 1 then LIWORK must be at least 1.
!>          If JOBZ  = 'V' 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 sizes of the WORK and
!>          IWORK arrays, returns these values as the first entries of
!>          the WORK and IWORK arrays, and no error message related to
!>          LWORK or LIWORK is issued by XERBLA.
!>

INFO

!>          INFO is INTEGER
!>          = 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 E did not converge to zero.
!>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

subroutine sstevd (character jobz, integer n, real, dimension( * ) d, real, dimension( * ) e, real, dimension( ldz, * ) z, integer ldz, real, dimension( * ) work, integer lwork, integer, dimension( * ) iwork, integer liwork, integer info)¶

SSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices