CXML
        	    
LAPACK version 3.0
zgtcon(3)

PURPOSE
  ZGTCON - estimate the reciprocal of the condition number of a complex
  tridiagonal matrix A using the LU factorization as computed by ZGTTRF

SYNTAX
  SUBROUTINE ZGTCON( NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, INFO
		     )

      CHARACTER	     NORM

      INTEGER	     INFO, N

      DOUBLE	     PRECISION ANORM, RCOND

      INTEGER	     IPIV( * )

      COMPLEX*16     D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )

DESCRIPTION
  ZGTCON estimates the reciprocal of the condition number of a complex
  tridiagonal matrix A using the LU factorization as computed by ZGTTRF.  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
  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.

  DL	  (input) COMPLEX*16 array, dimension (N-1)
	  The (n-1) multipliers that define the matrix L from the LU
	  factorization of A as computed by ZGTTRF.

  D	  (input) COMPLEX*16 array, dimension (N)
	  The n diagonal elements of the upper triangular matrix U from the
	  LU factorization of A.

  DU	  (input) COMPLEX*16 array, dimension (N-1)
	  The (n-1) elements of the first superdiagonal of U.

  DU2	  (input) COMPLEX*16 array, dimension (N-2)
	  The (n-2) elements of the second superdiagonal of U.

  IPIV	  (input) 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	  (input) DOUBLE PRECISION
	  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) 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) computed in this routine.

  WORK	  (workspace) COMPLEX*16 array, dimension (2*N)

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