dlaqgb()

subroutine dlaqgb	(	integer	m,
		integer	n,
		integer	kl,
		integer	ku,
		double precision, dimension( ldab, * )	ab,
		integer	ldab,
		double precision, dimension( * )	r,
		double precision, dimension( * )	c,
		double precision	rowcnd,
		double precision	colcnd,
		double precision	amax,
		character	equed
	)

DLAQGB scales a general band matrix, using row and column scaling factors computed by sgbequ.

Download DLAQGB + dependencies [TGZ] [ZIP] [TXT]

Purpose:

 DLAQGB equilibrates a general M by N band matrix A with KL
 subdiagonals and KU superdiagonals using the row and scaling factors
 in the vectors R and C.

Parameters

[in]	M	M is INTEGER The number of rows of the matrix A. M >= 0.
[in]	N	N is INTEGER The number of columns of the matrix A. N >= 0.
[in]	KL	KL is INTEGER The number of subdiagonals within the band of A. KL >= 0.
[in]	KU	KU is INTEGER The number of superdiagonals within the band of A. KU >= 0.
[in,out]	AB	AB is DOUBLE PRECISION array, dimension (LDAB,N) On entry, the matrix A in band storage, in rows 1 to KL+KU+1. The j-th column of A is stored in the j-th column of the array AB as follows: AB(ku+1+i-j,j) = A(i,j) for max(1,j-ku)<=i<=min(m,j+kl) On exit, the equilibrated matrix, in the same storage format as A. See EQUED for the form of the equilibrated matrix.
[in]	LDAB	LDAB is INTEGER The leading dimension of the array AB. LDA >= KL+KU+1.
[in]	R	R is DOUBLE PRECISION array, dimension (M) The row scale factors for A.
[in]	C	C is DOUBLE PRECISION array, dimension (N) The column scale factors for A.
[in]	ROWCND	ROWCND is DOUBLE PRECISION Ratio of the smallest R(i) to the largest R(i).
[in]	COLCND	COLCND is DOUBLE PRECISION Ratio of the smallest C(i) to the largest C(i).
[in]	AMAX	AMAX is DOUBLE PRECISION Absolute value of largest matrix entry.
[out]	EQUED	EQUED is CHARACTER*1 Specifies the form of equilibration that was done. = 'N': No equilibration = 'R': Row equilibration, i.e., A has been premultiplied by diag(R). = 'C': Column equilibration, i.e., A has been postmultiplied by diag(C). = 'B': Both row and column equilibration, i.e., A has been replaced by diag(R) * A * diag(C).

Internal Parameters:

  THRESH is a threshold value used to decide if row or column scaling
  should be done based on the ratio of the row or column scaling
  factors.  If ROWCND < THRESH, row scaling is done, and if
  COLCND < THRESH, column scaling is done.

  LARGE and SMALL are threshold values used to decide if row scaling
  should be done based on the absolute size of the largest matrix
  element.  If AMAX > LARGE or AMAX < SMALL, row scaling is done.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 157 of file dlaqgb.f.

*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          EQUED
      INTEGER            KL, KU, LDAB, M, N
      DOUBLE PRECISION   AMAX, COLCND, ROWCND
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   AB( LDAB, * ), C( * ), R( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ONE, THRESH
      parameter( one = 1.0d+0, thresh = 0.1d+0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I, J
      DOUBLE PRECISION   CJ, LARGE, SMALL
*     ..
*     .. External Functions ..
      DOUBLE PRECISION   DLAMCH
      EXTERNAL           dlamch
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          max, min
*     ..
*     .. Executable Statements ..
*
*     Quick return if possible
*
      IF( m.LE.0 .OR. n.LE.0 ) THEN
         equed = 'N'
         RETURN
      END IF
*
*     Initialize LARGE and SMALL.
*
      small = dlamch( 'Safe minimum' ) / dlamch( 'Precision' )
      large = one / small
*
      IF( rowcnd.GE.thresh .AND. amax.GE.small .AND. amax.LE.large )
     $     THEN
*
*        No row scaling
*
         IF( colcnd.GE.thresh ) THEN
*
*           No column scaling
*
            equed = 'N'
         ELSE
*
*           Column scaling
*
            DO 20 j = 1, n
               cj = c( j )
               DO 10 i = max( 1, j-ku ), min( m, j+kl )
                  ab( ku+1+i-j, j ) = cj*ab( ku+1+i-j, j )
   10          CONTINUE
   20       CONTINUE
            equed = 'C'
         END IF
      ELSE IF( colcnd.GE.thresh ) THEN
*
*        Row scaling, no column scaling
*
         DO 40 j = 1, n
            DO 30 i = max( 1, j-ku ), min( m, j+kl )
               ab( ku+1+i-j, j ) = r( i )*ab( ku+1+i-j, j )
   30       CONTINUE
   40    CONTINUE
         equed = 'R'
      ELSE
*
*        Row and column scaling
*
         DO 60 j = 1, n
            cj = c( j )
            DO 50 i = max( 1, j-ku ), min( m, j+kl )
               ab( ku+1+i-j, j ) = cj*r( i )*ab( ku+1+i-j, j )
   50       CONTINUE
   60    CONTINUE
         equed = 'B'
      END IF
*
      RETURN
*
*     End of DLAQGB
*

Here is the caller graph for this function: