Previous: sgebrd Up: ../lapack-s.html Next: sgeequ

sgecon

 NAME
      SGECON - estimate the reciprocal of the condition number of
      a general real matrix A, in either the 1-norm or the
      infinity-norm, using the LU factorization computed by SGETRF

 SYNOPSIS
      SUBROUTINE SGECON( NORM, N, A, LDA, ANORM, RCOND, WORK,
                         IWORK, INFO )

          CHARACTER      NORM

          INTEGER        INFO, LDA, N

          REAL           ANORM, RCOND

          INTEGER        IWORK( * )

          REAL           A( LDA, * ), WORK( * )

 PURPOSE
      SGECON estimates the reciprocal of the condition number of a
      general real matrix A, in either the 1-norm or the
      infinity-norm, using the LU factorization computed by
      SGETRF.

      An estimate is obtained for norm(inv(A)), and 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.

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

      A       (input) REAL array, dimension (LDA,N)
              The factors L and U from the factorization A = P*L*U
              as computed by SGETRF.

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

      ANORM   (input) REAL
              If NORM = '1' or 'O', the 1-norm of the original
              matrix A.  If NORM = 'I', the infinity-norm of the
              original matrix A.

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

      WORK    (workspace) REAL array, dimension (4*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