zsytri2()

subroutine zsytri2	(	character	uplo,
		integer	n,
		complex*16, dimension( lda, * )	a,
		integer	lda,
		integer, dimension( * )	ipiv,
		complex*16, dimension( * )	work,
		integer	lwork,
		integer	info )

ZSYTRI2

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Purpose:

!>
!> ZSYTRI2 computes the inverse of a COMPLEX*16 symmetric indefinite matrix
!> A using the factorization A = U*D*U**T or A = L*D*L**T computed by
!> ZSYTRF. ZSYTRI2 sets the LEADING DIMENSION of the workspace
!> before calling ZSYTRI2X that actually computes the inverse.
!> 

Parameters

[in]	UPLO	!> UPLO is CHARACTER*1 !> Specifies whether the details of the factorization are stored !> as an upper or lower triangular matrix. !> = 'U': Upper triangular, form is A = U*D*U**T; !> = 'L': Lower triangular, form is A = L*D*L**T. !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in,out]	A	!> A is COMPLEX*16 array, dimension (LDA,N) !> On entry, the block diagonal matrix D and the multipliers !> used to obtain the factor U or L as computed by ZSYTRF. !> !> On exit, if INFO = 0, the (symmetric) inverse of the original !> matrix. If UPLO = 'U', the upper triangular part of the !> inverse is formed and the part of A below the diagonal is not !> referenced; if UPLO = 'L' the lower triangular part of the !> inverse is formed and the part of A above the diagonal is !> not referenced. !>
[in]	LDA	!> LDA is INTEGER !> The leading dimension of the array A. LDA >= max(1,N). !>
[in]	IPIV	!> IPIV is INTEGER array, dimension (N) !> Details of the interchanges and the block structure of D !> as determined by ZSYTRF. !>
[out]	WORK	!> WORK is COMPLEX*16 array, dimension (N+NB+1)*(NB+3) !>
[in]	LWORK	!> LWORK is INTEGER !> The dimension of the array WORK. !> WORK is size >= (N+NB+1)*(NB+3) !> If LDWORK = -1, then a workspace query is assumed; the routine !> 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 LDWORK is issued by XERBLA. !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !> > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its !> inverse could not be computed. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 124 of file zsytri2.f.

*
*  -- LAPACK computational routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          UPLO
      INTEGER            INFO, LDA, LWORK, N
*     ..
*     .. Array Arguments ..
      INTEGER            IPIV( * )
      COMPLEX*16         A( LDA, * ), WORK( * )
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      LOGICAL            UPPER, LQUERY
      INTEGER            MINSIZE, NBMAX
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      INTEGER            ILAENV
      EXTERNAL           lsame, ilaenv
*     ..
*     .. External Subroutines ..
      EXTERNAL           zsytri, zsytri2x, xerbla
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
      info = 0
      upper = lsame( uplo, 'U' )
      lquery = ( lwork.EQ.-1 )
*     Get blocksize
      nbmax = ilaenv( 1, 'ZSYTRI2', uplo, n, -1, -1, -1 )
      IF ( nbmax .GE. n ) THEN
         minsize = n
      ELSE
         minsize = (n+nbmax+1)*(nbmax+3)
      END IF
*
      IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
         info = -1
      ELSE IF( n.LT.0 ) THEN
         info = -2
      ELSE IF( lda.LT.max( 1, n ) ) THEN
         info = -4
      ELSE IF (lwork .LT. minsize .AND. .NOT.lquery ) THEN
         info = -7
      END IF
*
*     Quick return if possible
*
*
      IF( info.NE.0 ) THEN
         CALL xerbla( 'ZSYTRI2', -info )
         RETURN
      ELSE IF( lquery ) THEN
         work(1)=minsize
         RETURN
      END IF
      IF( n.EQ.0 )
     $   RETURN
 
      IF( nbmax .GE. n ) THEN
         CALL zsytri( uplo, n, a, lda, ipiv, work, info )
      ELSE
         CALL zsytri2x( uplo, n, a, lda, ipiv, work, nbmax, info )
      END IF
      RETURN
*
*     End of ZSYTRI2
*

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