Provided by: liblapack-doc_3.3.1-1_all #### NAME

```       LAPACK-3  -  computes  the  inverse  of  a  real  symmetric  indefinite matrix A using the
factorization A = U*D*U**T or A = L*D*L**T computed by DSYTRF

```

#### SYNOPSIS

```       SUBROUTINE DSYTRI2X( UPLO, N, A, LDA, IPIV, WORK, NB, INFO )

CHARACTER        UPLO

INTEGER          INFO, LDA, N, NB

INTEGER          IPIV( * )

DOUBLE           PRECISION A( LDA, * ), WORK( N+NB+1,* )

```

#### PURPOSE

```       DSYTRI2X computes  the  inverse  of  a  real  symmetric  indefinite  matrix  A  using  the
factorization A = U*D*U**T or A = L*D*L**T computed by DSYTRF.

```

#### ARGUMENTS

```        UPLO    (input) 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.

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

A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, the NNB 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.

LDA     (input) INTEGER
The leading dimension of the array A.  LDA >= max(1,N).

IPIV    (input) INTEGER array, dimension (N)
Details of the interchanges and the NNB structure of D
as determined by DSYTRF.

WORK    (workspace) DOUBLE PRECISION array, dimension (N+NNB+1,NNB+3)

NB      (input) INTEGER
Block size

INFO    (output) 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.

LAPACK routine (version 3.3.1)             April 2011                          DSYTRI2X(3lapack)
```