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.

AP      (input/output) DOUBLE PRECISION 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    (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.

  —  LAPACK version 2.0  —  08 October 1994