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stev(3) Library Functions Manual stev(3)

NAME

stev - stev: eig, QR iteration

SYNOPSIS

Functions


subroutine DSTEV (jobz, n, d, e, z, ldz, work, info)
DSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices subroutine SSTEV (jobz, n, d, e, z, ldz, work, info)
SSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

Detailed Description

Function Documentation

subroutine DSTEV (character jobz, integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer info)

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

Purpose:

!>
!> DSTEV computes all eigenvalues and, optionally, eigenvectors of a
!> real symmetric tridiagonal matrix A.
!>

Parameters

JOBZ 

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

N

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

D

!>          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

!>          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

!>          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 (max(1,2*N-2))
!>          If JOBZ = 'N', WORK is not referenced.
!>

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.

Definition at line 115 of file dstev.f.

subroutine SSTEV (character jobz, integer n, real, dimension( * ) d, real, dimension( * ) e, real, dimension( ldz, * ) z, integer ldz, real, dimension( * ) work, integer info)

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

Purpose:

!>
!> SSTEV computes all eigenvalues and, optionally, eigenvectors of a
!> real symmetric tridiagonal matrix A.
!>

Parameters

JOBZ 

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

N

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

D

!>          D is REAL 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

!>          E is REAL 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

!>          Z is REAL 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 REAL array, dimension (max(1,2*N-2))
!>          If JOBZ = 'N', WORK is not referenced.
!>

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.

Definition at line 115 of file sstev.f.

Author

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