zsteqr.f man page

zsteqr.f —



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

Function/Subroutine Documentation

subroutine zsteqr (characterCOMPZ, integerN, double precision, dimension( * )D, double precision, dimension( * )E, complex*16, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integerINFO)



 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.


          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 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 is DOUBLE PRECISION array, dimension (N-1)
          On entry, the (n-1) subdiagonal elements of the tridiagonal
          On exit, E has been destroyed.


          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 is INTEGER
          The leading dimension of the array Z.  LDZ >= 1, and if
          eigenvectors are desired, then  LDZ >= max(1,N).


          WORK is DOUBLE PRECISION 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

NAG Ltd.


November 2011

Definition at line 133 of file zsteqr.f.


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Referenced By

zsteqr(3) is an alias of zsteqr.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK