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template<typename T>
void pptri(char *uplo, integer *n, T *ap, integer *info)# PPTRI computes the inverse of a real symmetric matrix.
Purpose:
PPTRI computes the inverse of a real symmetric positive definite matrix A using the Cholesky factorization A = U**T*U or A = L*L**T computed by PPTRF.
- Parameters:
UPLO – [in]
UPLO is CHARACTER*1
= ‘U’: Upper triangular factor is stored in AP;
= ‘L’: Lower triangular factor is stored in AP.N – [in]
N is INTEGER
The order of the matrix A. N >= 0.
AP – [inout]
AP is REAL array, dimension (N*(N+1)/2)
On entry, the triangular factor U or L from the Cholesky factorization A = U**T*U or A = L*L**T, packed columnwise as a linear array. The j-th column of U or L is stored in the array AP as follows:
if UPLO = ‘U’, AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
if UPLO = ‘L’, AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
On exit, the upper or lower triangle of the (symmetric) inverse of A, overwriting the input factor U or L.INFO – [out]
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: if INFO = i, the (i,i) element of the factor U or L is zero, and the inverse could not be computed.