SLAQGB(l) ) SLAQGB(l)
SLAQGB - equilibrate a general M by N band matrix A with KL subdiagonals and KU superdiag-
onals using the row and scaling factors in the vectors R and C
SUBROUTINE SLAQGB( M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, EQUED )
INTEGER KL, KU, LDAB, M, N
REAL AMAX, COLCND, ROWCND
REAL AB( LDAB, * ), C( * ), R( * )
SLAQGB equilibrates a general M by N band matrix A with KL subdiagonals and KU superdiago-
nals using the row and scaling factors in the vectors R and C.
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.
KL (input) INTEGER
The number of subdiagonals within the band of A. KL >= 0.
KU (input) INTEGER
The number of superdiagonals within the band of A. KU >= 0.
AB (input/output) REAL 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)
On exit, the equilibrated matrix, in the same storage format as A. See EQUED for
the form of the equilibrated matrix.
LDAB (input) INTEGER
The leading dimension of the array AB. LDA >= KL+KU+1.
R (output) REAL array, dimension (M)
The row scale factors for A.
C (output) REAL array, dimension (N)
The column scale factors for A.
ROWCND (output) REAL
Ratio of the smallest R(i) to the largest R(i).
COLCND (output) REAL
Ratio of the smallest C(i) to the largest C(i).
AMAX (input) REAL
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row and column equilibration, i.e., A has been replaced by diag(R) * A * diag(C).
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.
LAPACK version 3.0 15 June 2000 SLAQGB(l)