Previous: dtgsja Up: ../lapack-d.html Next: dtprfs

dtpcon

 NAME
      DTPCON - estimate the reciprocal of the condition number of
      a packed triangular matrix A, in either the 1-norm or the
      infinity-norm

 SYNOPSIS
      SUBROUTINE DTPCON( NORM, UPLO, DIAG, N, AP, RCOND, WORK,
                         IWORK, INFO )

          CHARACTER      DIAG, NORM, UPLO

          INTEGER        INFO, N

          DOUBLE         PRECISION RCOND

          INTEGER        IWORK( * )

          DOUBLE         PRECISION AP( * ), WORK( * )

 PURPOSE
      DTPCON estimates the reciprocal of the condition number of a
      packed triangular matrix A, in either the 1-norm or the
      infinity-norm.

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

 ARGUMENTS
      NORM    (input) CHARACTER*1
              Specifies whether the 1-norm condition number or the
              infinity-norm condition number is required:
              = '1' or 'O':  1-norm;
              = 'I':         Infinity-norm.

      UPLO    (input) CHARACTER*1
              = 'U':  A is upper triangular;
              = 'L':  A is lower triangular.

      DIAG    (input) CHARACTER*1
              = 'N':  A is non-unit triangular;
              = 'U':  A is unit triangular.

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

      AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
              The upper or lower triangular matrix A, packed
              columnwise in a linear array.  The j-th column of A
              is stored in the array AP as follows: if UPLO = 'U',

              AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO =
              'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
              If DIAG = 'U', the diagonal elements of A are not
              referenced and are assumed to be 1.

      RCOND   (output) DOUBLE PRECISION
              The reciprocal of the condition number of the matrix
              A, computed as RCOND = 1/(norm(A) * norm(inv(A))).

      WORK    (workspace) DOUBLE PRECISION array, dimension (3*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