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zsteqr.f(3) LAPACK zsteqr.f(3)

zsteqr.f -


subroutine zsteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
 
ZSTEQR

ZSTEQR
Purpose:
 ZSTEQR 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 ZHETRD or ZHPTRD or ZHBTRD has been used to reduce this
 matrix to tridiagonal form.
Parameters:
COMPZ
          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
                  matrix.
N
          N is INTEGER
          The order of the matrix.  N >= 0.
D
          D is DOUBLE PRECISION array, dimension (N)
          On entry, the diagonal elements of the tridiagonal matrix.
          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.
          On exit, E has been destroyed.
Z
          Z is COMPLEX*16 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
          LDZ is INTEGER
          The leading dimension of the array Z.  LDZ >= 1, and if
          eigenvectors are desired, then  LDZ >= max(1,N).
WORK
          WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2))
          If COMPZ = 'N', then WORK is not referenced.
INFO
          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
                matrix.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 133 of file zsteqr.f.

Generated automatically by Doxygen for LAPACK from the source code.
Sat Nov 16 2013 Version 3.4.2

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