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.

UPLO

          UPLO is CHARACTER*1


          = 'U':  Upper triangular factor is stored in AP;


          = 'L':  Lower triangular factor is stored in AP.

N

          N is INTEGER


          The order of the matrix A.  N >= 0.

AP

          AP is 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

          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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016