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zstedc.f(3)				      LAPACK				      zstedc.f(3)

NAME
       zstedc.f -

SYNOPSIS
   Functions/Subroutines
       subroutine zstedc (COMPZ, N, D, E, Z, LDZ, WORK, LWORK, RWORK, LRWORK, IWORK, LIWORK,
	   INFO)
	   ZSTEDC

Function/Subroutine Documentation
   subroutine zstedc (characterCOMPZ, integerN, double precision, dimension( * )D, double
       precision, dimension( * )E, complex*16, dimension( ldz, * )Z, integerLDZ, complex*16,
       dimension( * )WORK, integerLWORK, double precision, dimension( * )RWORK, integerLRWORK,
       integer, dimension( * )IWORK, integerLIWORK, integerINFO)
       ZSTEDC

       Purpose:

	    ZSTEDC computes all eigenvalues and, optionally, eigenvectors of a
	    symmetric tridiagonal matrix using the divide and conquer 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.

	    This code makes very mild assumptions about floating point
	    arithmetic. It will work on machines with a guard digit in
	    add/subtract, or on those binary machines without guard digits
	    which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or Cray-2.
	    It could conceivably fail on hexadecimal or decimal machines
	    without guard digits, but we know of none.	See DLAED3 for details.

       Parameters:
	   COMPZ

		     COMPZ is CHARACTER*1
		     = 'N':  Compute eigenvalues only.
		     = 'I':  Compute eigenvectors of tridiagonal matrix also.
		     = 'V':  Compute eigenvectors of original Hermitian matrix
			     also.  On entry, Z contains the unitary matrix used
			     to reduce the original matrix to tridiagonal form.

	   N

		     N is INTEGER
		     The dimension of the symmetric tridiagonal 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 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.
		     If eigenvectors are desired, then LDZ >= max(1,N).

	   WORK

		     WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
		     On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

	   LWORK

		     LWORK is INTEGER
		     The dimension of the array WORK.
		     If COMPZ = 'N' or 'I', or N <= 1, LWORK must be at least 1.
		     If COMPZ = 'V' and N > 1, LWORK must be at least N*N.
		     Note that for COMPZ = 'V', then if N is less than or
		     equal to the minimum divide size, usually 25, then LWORK need
		     only be 1.

		     If LWORK = -1, then a workspace query is assumed; the routine
		     only calculates the optimal sizes of the WORK, RWORK and
		     IWORK arrays, returns these values as the first entries of
		     the WORK, RWORK and IWORK arrays, and no error message
		     related to LWORK or LRWORK or LIWORK is issued by XERBLA.

	   RWORK

		     RWORK is DOUBLE PRECISION array,
						    dimension (LRWORK)
		     On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.

	   LRWORK

		     LRWORK is INTEGER
		     The dimension of the array RWORK.
		     If COMPZ = 'N' or N <= 1, LRWORK must be at least 1.
		     If COMPZ = 'V' and N > 1, LRWORK must be at least
				    1 + 3*N + 2*N*lg N + 4*N**2 ,
				    where lg( N ) = smallest integer k such
				    that 2**k >= N.
		     If COMPZ = 'I' and N > 1, LRWORK must be at least
				    1 + 4*N + 2*N**2 .
		     Note that for COMPZ = 'I' or 'V', then if N is less than or
		     equal to the minimum divide size, usually 25, then LRWORK
		     need only be max(1,2*(N-1)).

		     If LRWORK = -1, then a workspace query is assumed; the
		     routine only calculates the optimal sizes of the WORK, RWORK
		     and IWORK arrays, returns these values as the first entries
		     of the WORK, RWORK and IWORK arrays, and no error message
		     related to LWORK or LRWORK 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 COMPZ = 'N' or N <= 1, LIWORK must be at least 1.
		     If COMPZ = 'V' or N > 1,  LIWORK must be at least
					       6 + 6*N + 5*N*lg N.
		     If COMPZ = 'I' or N > 1,  LIWORK must be at least
					       3 + 5*N .
		     Note that for COMPZ = 'I' or 'V', then if N is less than or
		     equal to the minimum divide size, usually 25, then LIWORK
		     need only be 1.

		     If LIWORK = -1, then a workspace query is assumed; the
		     routine only calculates the optimal sizes of the WORK, RWORK
		     and IWORK arrays, returns these values as the first entries
		     of the WORK, RWORK and IWORK arrays, and no error message
		     related to LWORK or LRWORK 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:  The algorithm failed to compute an eigenvalue while
			   working on the submatrix lying in rows and columns
			   INFO/(N+1) through mod(INFO,N+1).

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Contributors:
	   Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

       Definition at line 213 of file zstedc.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2				 Tue Sep 25 2012			      zstedc.f(3)
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