csteqr.f(3) LAPACK csteqr.f(3)NAME
subroutine csteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
subroutine csteqr (characterCOMPZ, integerN, real, dimension( * )D, real,
dimension( * )E, complex, dimension( ldz, * )Z, integerLDZ, real,
dimension( * )WORK, integerINFO)
CSTEQR computes all eigenvalues and, optionally, eigenvectors of a
symmetric tridiagonal matrix using the implicit QL or QR method.
The eigenvectors of a full or band complex Hermitian matrix can also
be found if CHETRD or CHPTRD or CHBTRD has been used to reduce this
matrix to tridiagonal form.
COMPZ is CHARACTER*1
= 'N': Compute eigenvalues only.
= 'V': Compute eigenvalues and eigenvectors of the original
Hermitian matrix. On entry, Z must contain the
unitary matrix used to reduce the original matrix
to tridiagonal form.
= 'I': Compute eigenvalues and eigenvectors of the
tridiagonal matrix. Z is initialized to the identity
N is INTEGER
The order of the matrix. N >= 0.
D is REAL array, dimension (N)
On entry, the diagonal elements of the tridiagonal matrix.
On exit, if INFO = 0, the eigenvalues in ascending order.
E is REAL array, dimension (N-1)
On entry, the (n-1) subdiagonal elements of the tridiagonal
On exit, E has been destroyed.
Z is COMPLEX array, dimension (LDZ, N)
On entry, if COMPZ = 'V', then Z contains the unitary
matrix used in the reduction to tridiagonal form.
On exit, if INFO = 0, then if COMPZ = 'V', Z contains the
orthonormal eigenvectors of the original Hermitian matrix,
and if COMPZ = 'I', Z contains the orthonormal eigenvectors
of the symmetric tridiagonal matrix.
If COMPZ = 'N', then Z is not referenced.
LDZ is INTEGER
The leading dimension of the array Z. LDZ >= 1, and if
eigenvectors are desired, then LDZ >= max(1,N).
WORK is REAL array, dimension (max(1,2*N-2))
If COMPZ = 'N', then WORK is not referenced.
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: the algorithm has failed to find all the eigenvalues in
a total of 30*N iterations; if INFO = i, then i
elements of E have not converged to zero; on exit, D
and E contain the elements of a symmetric tridiagonal
matrix which is unitarily similar to the original
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
Definition at line 133 of file csteqr.f.
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 csteqr.f(3)