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LAPACK version 3.0
sspevd(3)

PURPOSE
  SSPEVD - compute all the eigenvalues and, optionally, eigenvectors of a
  real symmetric matrix A in packed storage

SYNTAX
  SUBROUTINE SSPEVD( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, LWORK, IWORK,
		     LIWORK, INFO )

      CHARACTER	     JOBZ, UPLO

      INTEGER	     INFO, LDZ, LIWORK, LWORK, N

      INTEGER	     IWORK( * )

      REAL	     AP( * ), W( * ), WORK( * ), Z( LDZ, * )

DESCRIPTION
  SSPEVD computes all the eigenvalues and, optionally, eigenvectors of a real
  symmetric matrix A in packed storage. If eigenvectors are desired, it uses
  a divide and conquer algorithm.

  The divide and conquer algorithm 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.

ARGUMENTS
  JOBZ	  (input) CHARACTER*1
	  = 'N':  Compute eigenvalues only;
	  = 'V':  Compute eigenvalues and eigenvectors.

  UPLO	  (input) CHARACTER*1
	  = 'U':  Upper triangle of A is stored;
	  = 'L':  Lower triangle of A is stored.

  N	  (input) INTEGER
	  The order of the matrix A.  N >= 0.

  AP	  (input/output) REAL array, dimension (N*(N+1)/2)
	  On entry, the upper or lower triangle of the symmetric matrix A,
	  packed columnwise in a linear array.	The j-th column of A is
	  stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2)
	  = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) =
	  A(i,j) for j<=i<=n.

	  On exit, AP is overwritten by values generated during the reduction
	  to tridiagonal form.	If UPLO = 'U', the diagonal and first
	  superdiagonal of the tridiagonal matrix T overwrite the
	  corresponding elements of A, and if UPLO = 'L', the diagonal and
	  first subdiagonal of T overwrite the corresponding elements of A.

  W	  (output) REAL array, dimension (N)
	  If INFO = 0, the eigenvalues in ascending order.

  Z	  (output) 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 W(i).  If JOBZ = 'N', then Z is not
	  referenced.

  LDZ	  (input) INTEGER
	  The leading dimension of the array Z.	 LDZ >= 1, and if JOBZ = 'V',
	  LDZ >= max(1,N).

  WORK	  (workspace/output) REAL array,
	  dimension (LWORK) On exit, if INFO = 0, WORK(1) returns the optimal
	  LWORK.

  LWORK	  (input) INTEGER
	  The dimension of the array WORK.  If N <= 1,		     LWORK
	  must be at least 1.  If JOBZ = 'N' and N > 1, LWORK must be at
	  least 2*N.  If JOBZ = 'V' and N > 1, LWORK must be at least 1 + 6*N
	  + N**2.

	  If LWORK = -1, then a workspace query is assumed; the routine only
	  calculates the optimal size of the WORK array, returns this value
	  as the first entry of the WORK array, and no error message related
	  to LWORK is issued by XERBLA.

  IWORK	  (workspace/output) INTEGER array, dimension (LIWORK)
	  On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

  LIWORK  (input) INTEGER
	  The dimension of the array IWORK.  If JOBZ  = 'N' or N <= 1, LIWORK
	  must be at least 1.  If JOBZ	= 'V' and N > 1, LIWORK must be at
	  least 3 + 5*N.

	  If LIWORK = -1, then a workspace query is assumed; the routine only
	  calculates the optimal size of the IWORK array, returns this value
	  as the first entry of the IWORK array, and no error message related
	  to LIWORK is issued by XERBLA.

  INFO	  (output) 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 an intermediate tridiagonal form did not converge to
	  zero.