dspcon(3F)

NAME
     DSPCON - estimate the reciprocal of the condition number (in the 1-norm)
     of a real symmetric packed matrix A using the factorization A = U*D*U**T
     or A = L*D*L**T computed by DSPTRF

SYNOPSIS
     SUBROUTINE DSPCON( UPLO, N, AP, IPIV, ANORM, RCOND, WORK, IWORK, INFO )

         CHARACTER      UPLO

         INTEGER        INFO, N

         DOUBLE         PRECISION ANORM, RCOND

         INTEGER        IPIV( * ), IWORK( * )

         DOUBLE         PRECISION AP( * ), WORK( * )

PURPOSE
     DSPCON estimates the reciprocal of the condition number (in the 1-norm)
     of a real symmetric packed matrix A using the factorization A = U*D*U**T
     or A = L*D*L**T computed by DSPTRF.

     An estimate is obtained for norm(inv(A)), and the reciprocal of the
     condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).


ARGUMENTS
     UPLO    (input) CHARACTER*1
             Specifies whether the details of the factorization are stored as
             an upper or lower triangular matrix.  = 'U':  Upper triangular,
             form is A = U*D*U**T;
             = 'L':  Lower triangular, form is A = L*D*L**T.

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

     AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
             The block diagonal matrix D and the multipliers used to obtain
             the factor U or L as computed by DSPTRF, stored as a packed
             triangular matrix.

     IPIV    (input) INTEGER array, dimension (N)
             Details of the interchanges and the block structure of D as
             determined by DSPTRF.

     ANORM   (input) DOUBLE PRECISION
             The 1-norm of the original matrix A.

     RCOND   (output) 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    (workspace) DOUBLE PRECISION array, dimension (2*N)

     IWORK    (workspace) INTEGER array, dimension (N)

     INFO    (output) INTEGER
             = 0:  successful exit
             < 0:  if INFO = -i, the i-th argument had an illegal value