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# dpptri

```
NAME
DPPTRI - compute 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 DPPTRF

SYNOPSIS
SUBROUTINE DPPTRI( UPLO, N, AP, INFO )

CHARACTER      UPLO

INTEGER        INFO, N

DOUBLE         PRECISION AP( * )

PURPOSE
DPPTRI 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 DPPTRF.

ARGUMENTS
UPLO    (input) CHARACTER*1
= 'U':  Upper triangular factor is stored in AP;
= 'L':  Lower triangular factor is stored in AP.

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

(N*(N+1)/2)
AP      (input/output) DOUBLE PRECISION array, dimension
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 fol-
lows: 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 (sym-
metric) inverse of A, overwriting the input factor U
or L.

INFO    (output) 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.
```