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dsycon

 NAME
      DSYCON - estimate the reciprocal of the condition number (in
      the 1-norm) of a real symmetric matrix A using the factori-
      zation A = U*D*U**T or A = L*D*L**T computed by DSYTRF

 SYNOPSIS
      SUBROUTINE DSYCON( UPLO, N, A, LDA, IPIV, ANORM, RCOND,
                         WORK, IWORK, INFO )

          CHARACTER      UPLO

          INTEGER        INFO, LDA, N

          DOUBLE         PRECISION ANORM, RCOND

          INTEGER        IPIV( * ), IWORK( * )

          DOUBLE         PRECISION A( LDA, * ), WORK( * )

 PURPOSE
      DSYCON estimates the reciprocal of the condition number (in
      the 1-norm) of a real symmetric matrix A using the factori-
      zation A = U*D*U**T or A = L*D*L**T computed by DSYTRF.

      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.

      A       (input) DOUBLE PRECISION array, dimension (LDA,N)
              The block diagonal matrix D and the multipliers used
              to obtain the factor U or L as computed by DSYTRF.

      LDA     (input) INTEGER
              The leading dimension of the array A.  LDA >=
              max(1,N).

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

      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) com-
              puted 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