dsytri2()

subroutine dsytri2	(	character	UPLO,
		integer	N,
		double precision, dimension( lda, * )	A,
		integer	LDA,
		integer, dimension( * )	IPIV,
		double precision, dimension( * )	WORK,
		integer	LWORK,
		integer	INFO
	)

DSYTRI2

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Purpose:

 DSYTRI2 computes the inverse of a DOUBLE PRECISION symmetric indefinite matrix
 A using the factorization A = U*D*U**T or A = L*D*L**T computed by
 DSYTRF. DSYTRI2 sets the LEADING DIMENSION of the workspace
 before calling DSYTRI2X 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 DOUBLE PRECISION 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 DSYTRF. 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 DSYTRF.
[out]	WORK	WORK is DOUBLE PRECISION 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 LWORK = -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 LWORK 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.

Date

November 2017

Definition at line 129 of file dsytri2.f.

*
*  -- LAPACK computational routine (version 3.8.0) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2017
*
*     .. Scalar Arguments ..
      CHARACTER          UPLO
      INTEGER            INFO, LDA, LWORK, N
*     ..
*     .. Array Arguments ..
      INTEGER            IPIV( * )
      DOUBLE PRECISION   A( LDA, * ), WORK( * )
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      LOGICAL            UPPER, LQUERY
      INTEGER            MINSIZE, NBMAX
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      INTEGER            ILAENV
      EXTERNAL           lsame, ilaenv
*     ..
*     .. External Subroutines ..
      EXTERNAL           dsytri, dsytri2x, xerbla
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
      info = 0
      upper = lsame( uplo, 'U' )
      lquery = ( lwork.EQ.-1 )
*     Get blocksize
      nbmax = ilaenv( 1, 'DSYTRI2', 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( 'DSYTRI2', -info )
         RETURN
      ELSE IF( lquery ) THEN
         work(1)=minsize
         RETURN
      END IF
      IF( n.EQ.0 )
     $   RETURN
 
      IF( nbmax .GE. n ) THEN
         CALL dsytri( uplo, n, a, lda, ipiv, work, info )
      ELSE
         CALL dsytri2x( uplo, n, a, lda, ipiv, work, nbmax, info )
      END IF
      RETURN
*
*     End of DSYTRI2
*

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