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DPBCON(3F)							    DPBCON(3F)


NAME    [Toc]    [Back]

     DPBCON - estimate the reciprocal of the condition number (in the 1-norm)
     of	a real symmetric positive definite band	matrix using the Cholesky
     factorization A = U**T*U or A = L*L**T computed by	DPBTRF

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	DPBCON(	UPLO, N, KD, AB, LDAB, ANORM, RCOND, WORK, IWORK, INFO
			)

	 CHARACTER	UPLO

	 INTEGER	INFO, KD, LDAB,	N

	 DOUBLE		PRECISION ANORM, RCOND

	 INTEGER	IWORK( * )

	 DOUBLE		PRECISION AB( LDAB, * ), WORK( * )

PURPOSE    [Toc]    [Back]

     DPBCON estimates the reciprocal of	the condition number (in the 1-norm)
     of	a real symmetric positive definite band	matrix using the Cholesky
     factorization A = U**T*U or A = L*L**T computed by	DPBTRF.

     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    [Toc]    [Back]

     UPLO    (input) CHARACTER*1
	     = 'U':  Upper triangular factor stored in AB;
	     = 'L':  Lower triangular factor stored in AB.

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

     KD	     (input) INTEGER
	     The number	of superdiagonals of the matrix	A if UPLO = 'U', or
	     the number	of subdiagonals	if UPLO	= 'L'.	KD >= 0.

     AB	     (input) DOUBLE PRECISION array, dimension (LDAB,N)
	     The triangular factor U or	L from the Cholesky factorization A =
	     U**T*U or A = L*L**T of the band matrix A,	stored in the first
	     KD+1 rows of the array.  The j-th column of U or L	is stored in
	     the j-th column of	the array AB as	follows:  if UPLO ='U',
	     AB(kd+1+i-j,j) = U(i,j) for max(1,j-kd)<=i<=j; if UPLO ='L',
	     AB(1+i-j,j)    = L(i,j) for j<=i<=min(n,j+kd).

     LDAB    (input) INTEGER
	     The leading dimension of the array	AB.  LDAB >= KD+1.





									Page 1






DPBCON(3F)							    DPBCON(3F)



     ANORM   (input) DOUBLE PRECISION
	     The 1-norm	(or infinity-norm) of the symmetric band 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) DOUBLE	PRECISION array, dimension (3*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
DPBCON(3F)							    DPBCON(3F)


NAME    [Toc]    [Back]

     DPBCON - estimate the reciprocal of the condition number (in the 1-norm)
     of	a real symmetric positive definite band	matrix using the Cholesky
     factorization A = U**T*U or A = L*L**T computed by	DPBTRF

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	DPBCON(	UPLO, N, KD, AB, LDAB, ANORM, RCOND, WORK, IWORK, INFO
			)

	 CHARACTER	UPLO

	 INTEGER	INFO, KD, LDAB,	N

	 DOUBLE		PRECISION ANORM, RCOND

	 INTEGER	IWORK( * )

	 DOUBLE		PRECISION AB( LDAB, * ), WORK( * )

PURPOSE    [Toc]    [Back]

     DPBCON estimates the reciprocal of	the condition number (in the 1-norm)
     of	a real symmetric positive definite band	matrix using the Cholesky
     factorization A = U**T*U or A = L*L**T computed by	DPBTRF.

     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    [Toc]    [Back]

     UPLO    (input) CHARACTER*1
	     = 'U':  Upper triangular factor stored in AB;
	     = 'L':  Lower triangular factor stored in AB.

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

     KD	     (input) INTEGER
	     The number	of superdiagonals of the matrix	A if UPLO = 'U', or
	     the number	of subdiagonals	if UPLO	= 'L'.	KD >= 0.

     AB	     (input) DOUBLE PRECISION array, dimension (LDAB,N)
	     The triangular factor U or	L from the Cholesky factorization A =
	     U**T*U or A = L*L**T of the band matrix A,	stored in the first
	     KD+1 rows of the array.  The j-th column of U or L	is stored in
	     the j-th column of	the array AB as	follows:  if UPLO ='U',
	     AB(kd+1+i-j,j) = U(i,j) for max(1,j-kd)<=i<=j; if UPLO ='L',
	     AB(1+i-j,j)    = L(i,j) for j<=i<=min(n,j+kd).

     LDAB    (input) INTEGER
	     The leading dimension of the array	AB.  LDAB >= KD+1.





									Page 1






DPBCON(3F)							    DPBCON(3F)



     ANORM   (input) DOUBLE PRECISION
	     The 1-norm	(or infinity-norm) of the symmetric band 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) DOUBLE	PRECISION array, dimension (3*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


									PPPPaaaaggggeeee 2222
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