DSYCON man page on IRIX

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DSYCON(3F)							    DSYCON(3F)

NAME
     DSYCON - estimate the reciprocal of the condition number (in the 1-norm)
     of a real symmetric matrix A using the factorization A = U*D*U**T or A =
     L*D*L**T computed by DSYTRF

SYNOPSIS
     SUBROUTINE DSYCON( UPLO, N, A, LDA, IPIV, ANORM, RCOND, WORK, IWORK, INFO
			)

	 CHARACTER	UPLO

	 INTEGER	INFO, LDA, N

	 DOUBLE		PRECISION ANORM, RCOND

	 INTEGER	IPIV( * ), IWORK( * )

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

PURPOSE
     DSYCON estimates the reciprocal of the condition number (in the 1-norm)
     of a real symmetric matrix A using the factorization A = U*D*U**T or A =
     L*D*L**T computed by DSYTRF.

     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
     UPLO    (input) CHARACTER*1
	     Specifies whether the details of the factorization are stored as
	     an upper or lower triangular matrix.  = 'U':  Upper triangular,
	     form is A = U*D*U**T;
	     = 'L':  Lower triangular, form is A = L*D*L**T.

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

     A	     (input) DOUBLE PRECISION array, dimension (LDA,N)
	     The block diagonal matrix D and the multipliers used to obtain
	     the factor U or L as computed by DSYTRF.

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

     IPIV    (input) INTEGER array, dimension (N)
	     Details of the interchanges and the block structure of D as
	     determined by DSYTRF.

     ANORM   (input) DOUBLE PRECISION
	     The 1-norm of the original matrix A.

									Page 1

DSYCON(3F)							    DSYCON(3F)

     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) DOUBLE PRECISION 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

									Page 2

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