cgtcon.f(3)

NAME
cgtcon.f

SYNOPSIS

  Functions/Subroutines
subroutine cgtcon (NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, INFO)
CGTCON

Function/Subroutine Documentation

  subroutine cgtcon (character NORM, integer N, complex, dimension( * ) DL, complex, dimension( * ) D, complex, dimension( * ) DU, complex, dimension( * ) DU2, integer, dimension( * ) IPIV, real ANORM, real RCOND, complex, dimension( * ) WORK, integer INFO)

Purpose:

     CGTCON estimates the reciprocal of the condition number of a complex
     tridiagonal matrix A using the LU factorization as computed by
     CGTTRF.
     An estimate is obtained for norm(inv(A)), and the reciprocal of the
     condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).

Parameters
    NORM

              NORM is 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

              N is INTEGER
              The order of the matrix A.  N >= 0.

    DL

              DL is COMPLEX array, dimension (N-1)
              The (n-1) multipliers that define the matrix L from the
              LU factorization of A as computed by CGTTRF.

    D

              D is COMPLEX array, dimension (N)
              The n diagonal elements of the upper triangular matrix U from
              the LU factorization of A.

    DU

              DU is COMPLEX array, dimension (N-1)
              The (n-1) elements of the first superdiagonal of U.

    DU2

              DU2 is COMPLEX array, dimension (N-2)
              The (n-2) elements of the second superdiagonal of U.

    IPIV

              IPIV is INTEGER array, dimension (N)
              The pivot indices; for 1 <= i <= n, row i of the matrix was
              interchanged with row IPIV(i).  IPIV(i) will always be either
              i or i+1; IPIV(i) = i indicates a row interchange was not
              required.

    ANORM

              ANORM is 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

              RCOND is REAL
              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

              WORK is COMPLEX array, dimension (2*N)

    INFO

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

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 139 of file cgtcon.f.

Author

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