Previous: dtptrs Up: ../lapack-d.html Next: dtrevc

dtrcon

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

 SYNOPSIS
      SUBROUTINE DTRCON( NORM, UPLO, DIAG, N, A, LDA, RCOND, WORK,
                         IWORK, INFO )

          CHARACTER      DIAG, NORM, UPLO

          INTEGER        INFO, LDA, N

          DOUBLE         PRECISION RCOND

          INTEGER        IWORK( * )

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

 PURPOSE
      DTRCON estimates the reciprocal of the condition number of a
      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.

      A       (input) DOUBLE PRECISION array, dimension (LDA,N)
              The triangular matrix A.  If UPLO = 'U', the leading
              N-by-N upper triangular part of the array A contains
              the upper triangular matrix, and the strictly lower

              triangular part of A is not referenced.  If UPLO =
              'L', the leading N-by-N lower triangular part of the
              array A contains the lower triangular matrix, and
              the strictly upper triangular part of A is not
              referenced.  If DIAG = 'U', the diagonal elements of
              A are also not referenced and are assumed to be 1.

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

      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