ssytri2.f −

**Functions/Subroutines**

subroutine **ssytri2** (UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO)

SSYTRI2

**subroutine ssytri2 (characterUPLO, integerN, real, dimension( lda, * )A, integerLDA, integer, dimension( * )IPIV, real, dimension( * )WORK, integerLWORK, integerINFO)
SSYTRI2**

**Purpose:**

SSYTRI2 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

SSYTRF. SSYTRI2 sets the LEADING DIMENSION of the workspace

before calling SSYTRI2X that actually computes the inverse.

**Parameters:**

*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.

*N*

N is INTEGER

The order of the matrix A. N >= 0.

*A*

A is REAL array, dimension (LDA,N)

On entry, the NB diagonal matrix D and the multipliers

used to obtain the factor U or L as computed by SSYTRF.

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*

LDA is INTEGER

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

*IPIV*

IPIV is INTEGER array, dimension (N)

Details of the interchanges and the NB structure of D

as determined by SSYTRF.

*WORK*

WORK is REAL array, dimension (N+NB+1)*(NB+3)

*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.

*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:**

September 2012

Definition at line 128 of file ssytri2.f.

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