SSPTRI computes the inverse of a real symmetric indefinite matrix


 A in packed storage using the factorization A = U*D*U**T or


 A = L*D*L**T computed by SSPTRF.

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.

AP

          AP is REAL array, dimension (N*(N+1)/2)


          On entry, the block diagonal matrix D and the multipliers


          used to obtain the factor U or L as computed by SSPTRF,


          stored as a packed triangular matrix.


          On exit, if INFO = 0, the (symmetric) inverse of the original


          matrix, stored as a packed triangular matrix. The j-th column


          of inv(A) is stored in the array AP as follows:


          if UPLO = 'U', AP(i + (j-1)*j/2) = inv(A)(i,j) for 1<=i<=j;


          if UPLO = 'L',


             AP(i + (j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

IPIV

          IPIV is INTEGER array, dimension (N)


          Details of the interchanges and the block structure of D


          as determined by SSPTRF.

WORK

          WORK is REAL array, dimension (N)

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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016