DPPCON estimates the reciprocal of the condition number (in the


 1-norm) of a real symmetric positive definite packed matrix using


 the Cholesky factorization A = U**T*U or A = L*L**T computed by


 DPPTRF.


 An estimate is obtained for norm(inv(A)), and the reciprocal of the


 condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).

UPLO

          UPLO is CHARACTER*1


          = 'U':  Upper triangle of A is stored;


          = 'L':  Lower triangle of A is stored.

N

          N is INTEGER


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

AP

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


          The triangular factor U or L from the Cholesky factorization


          A = U**T*U or A = L*L**T, packed columnwise in 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.

ANORM

          ANORM is DOUBLE PRECISION


          The 1-norm (or infinity-norm) of the symmetric matrix A.

RCOND

          RCOND is DOUBLE PRECISION


          The reciprocal of the condition number of the matrix A,


          computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an


          estimate of the 1-norm of inv(A) computed in this routine.

WORK

          WORK is DOUBLE PRECISION array, dimension (3*N)

IWORK

          IWORK is INTEGER array, dimension (N)

INFO

          INFO is INTEGER


          = 0:  successful exit


          < 0:  if INFO = -i, the i-th argument had an illegal value

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016