NAME

ssytri - compute 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

SYNOPSIS

  SUBROUTINE SSYTRI( UPLO, N, A, LDA, IPIVOT, WORK, INFO)
  CHARACTER * 1 UPLO
  INTEGER N, LDA, INFO
  INTEGER IPIVOT(*)
  REAL A(LDA,*), WORK(*)

  SUBROUTINE SSYTRI_64( UPLO, N, A, LDA, IPIVOT, WORK, INFO)
  CHARACTER * 1 UPLO
  INTEGER*8 N, LDA, INFO
  INTEGER*8 IPIVOT(*)
  REAL A(LDA,*), WORK(*)

F95 INTERFACE

  SUBROUTINE SYTRI( UPLO, [N], A, [LDA], IPIVOT, [WORK], [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER :: N, LDA, INFO
  INTEGER, DIMENSION(:) :: IPIVOT
  REAL, DIMENSION(:) :: WORK
  REAL, DIMENSION(:,:) :: A

  SUBROUTINE SYTRI_64( UPLO, [N], A, [LDA], IPIVOT, [WORK], [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER(8) :: N, LDA, INFO
  INTEGER(8), DIMENSION(:) :: IPIVOT
  REAL, DIMENSION(:) :: WORK
  REAL, DIMENSION(:,:) :: A

C INTERFACE

#include <sunperf.h>

void ssytri(char uplo, int n, float *a, int lda, int *ipivot, int *info);

void ssytri_64(char uplo, long n, float *a, long lda, long *ipivot, long *info);

PURPOSE

ssytri 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.

ARGUMENTS

UPLO (input)
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)
The order of the matrix A. N > = 0.
A (input/output)
On entry, the block 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 (input)
The leading dimension of the array A. LDA > = max(1,N).
IPIVOT (input)
Details of the interchanges and the block structure of D as determined by SSYTRF.
WORK (workspace)
dimension(N)

INFO (output)

 = 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.