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RedHat 9 (Linux i386) - man page for sgtcon (redhat section l)

SGTCON(l)					)					SGTCON(l)

NAME
       SGTCON  -  estimate  the reciprocal of the condition number of a real tridiagonal matrix A
       using the LU factorization as computed by SGTTRF

SYNOPSIS
       SUBROUTINE SGTCON( NORM, N, DL, D, DU, DU2, IPIV, ANORM, RCOND, WORK, IWORK, INFO )

	   CHARACTER	  NORM

	   INTEGER	  INFO, N

	   REAL 	  ANORM, RCOND

	   INTEGER	  IPIV( * ), IWORK( * )

	   REAL 	  D( * ), DL( * ), DU( * ), DU2( * ), WORK( * )

PURPOSE
       SGTCON estimates the reciprocal of the condition number of a  real  tridiagonal	matrix	A
       using  the  LU  factorization  as  computed  by	SGTTRF.   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 num-
	       ber is required:
	       = '1' or 'O':  1-norm;
	       = 'I':	      Infinity-norm.

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

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

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

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

       DU2     (input) REAL 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) 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/(ANORM * AINVNM), where AINVNM is an estimate of the 1-norm of  inv(A)  computed
	       in this routine.

       WORK    (workspace) REAL array, dimension (2*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

LAPACK version 3.0			   15 June 2000 				SGTCON(l)


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