
dgeequb.f(3) LAPACK dgeequb.f(3)
NAME
dgeequb.f 
SYNOPSIS
Functions/Subroutines
subroutine dgeequb (M, N, A, LDA, R, C, ROWCND, COLCND, AMAX, INFO)
DGEEQUB
Function/Subroutine Documentation
subroutine dgeequb (integerM, integerN, double precision, dimension( lda, * )A, integerLDA,
double precision, dimension( * )R, double precision, dimension( * )C, double
precisionROWCND, double precisionCOLCND, double precisionAMAX, integerINFO)
DGEEQUB
Purpose:
DGEEQUB computes row and column scalings intended to equilibrate an
MbyN matrix A and reduce its condition number. R returns the row
scale factors and C the column scale factors, chosen to try to make
the largest element in each row and column of the matrix B with
elements B(i,j)=R(i)*A(i,j)*C(j) have an absolute value of at most
the radix.
R(i) and C(j) are restricted to be a power of the radix between
SMLNUM = smallest safe number and BIGNUM = largest safe number. Use
of these scaling factors is not guaranteed to reduce the condition
number of A but works well in practice.
This routine differs from DGEEQU by restricting the scaling factors
to a power of the radix. Baring over and underflow, scaling by
these factors introduces no additional rounding errors. However, the
scaled entries' magnitured are no longer approximately 1 but lie
between sqrt(radix) and 1/sqrt(radix).
Parameters:
M
M is INTEGER
The number of rows of the matrix A. M >= 0.
N
N is INTEGER
The number of columns of the matrix A. N >= 0.
A
A is DOUBLE PRECISION array, dimension (LDA,N)
The MbyN matrix whose equilibration factors are
to be computed.
LDA
LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,M).
R
R is DOUBLE PRECISION array, dimension (M)
If INFO = 0 or INFO > M, R contains the row scale factors
for A.
C
C is DOUBLE PRECISION array, dimension (N)
If INFO = 0, C contains the column scale factors for A.
ROWCND
ROWCND is DOUBLE PRECISION
If INFO = 0 or INFO > M, ROWCND contains the ratio of the
smallest R(i) to the largest R(i). If ROWCND >= 0.1 and
AMAX is neither too large nor too small, it is not worth
scaling by R.
COLCND
COLCND is DOUBLE PRECISION
If INFO = 0, COLCND contains the ratio of the smallest
C(i) to the largest C(i). If COLCND >= 0.1, it is not
worth scaling by C.
AMAX
AMAX is DOUBLE PRECISION
Absolute value of largest matrix element. If AMAX is very
close to overflow or very close to underflow, the matrix
should be scaled.
INFO
INFO is INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, and i is
<= M: the ith row of A is exactly zero
> M: the (iM)th column of A is exactly zero
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 146 of file dgeequb.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dgeequb.f(3) 
