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SUBROUTINE DLAQGE( M, N, A, LDA, R, C, ROWCND, COLCND, AMAX,
$ EQUED )
*
* -- LAPACK auxiliary routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
CHARACTER EQUED
INTEGER LDA, M, N
DOUBLE PRECISION AMAX, COLCND, ROWCND
* ..
* .. Array Arguments ..
DOUBLE PRECISION A( LDA, * ), C( * ), R( * )
* ..
*
* Purpose
* =======
*
* DLAQGE equilibrates a general M by N matrix A using the row and
* column scaling factors in the vectors R and C.
*
* Arguments
* =========
*
* M (input) INTEGER
* The number of rows of the matrix A. M >= 0.
*
* N (input) INTEGER
* The number of columns of the matrix A. N >= 0.
*
* A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
* On entry, the M by N matrix A.
* On exit, the equilibrated matrix. See EQUED for the form of
* the equilibrated matrix.
*
* LDA (input) INTEGER
* The leading dimension of the array A. LDA >= max(M,1).
*
* R (input) DOUBLE PRECISION array, dimension (M)
* The row scale factors for A.
*
* C (input) DOUBLE PRECISION array, dimension (N)
* The column scale factors for A.
*
* ROWCND (input) DOUBLE PRECISION
* Ratio of the smallest R(i) to the largest R(i).
*
* COLCND (input) DOUBLE PRECISION
* Ratio of the smallest C(i) to the largest C(i).
*
* AMAX (input) DOUBLE PRECISION
* Absolute value of largest matrix entry.
*
* EQUED (output) 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.
*
* =====================================================================
*
* .. 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
* ..
* .. 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 = 1, M
A( I, J ) = CJ*A( I, 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 = 1, M
A( I, J ) = R( I )*A( I, J )
30 CONTINUE
40 CONTINUE
EQUED = 'R'
ELSE
*
* Row and column scaling
*
DO 60 J = 1, N
CJ = C( J )
DO 50 I = 1, M
A( I, J ) = CJ*R( I )*A( I, J )
50 CONTINUE
60 CONTINUE
EQUED = 'B'
END IF
*
RETURN
*
* End of DLAQGE
*
END
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