sgbequb.f(3) LAPACK sgbequb.f(3)
subroutine sgbequb (M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, INFO)
subroutine sgbequb (integerM, integerN, integerKL, integerKU, real, dimension( ldab, * )AB, integerLDAB, real, dimension( * )R, real,
dimension( * )C, realROWCND, realCOLCND, realAMAX, integerINFO)
SGBEQUB computes row and column scalings intended to equilibrate an
M-by-N 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
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 SGEEQU 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).
M is INTEGER
The number of rows of the matrix A. M >= 0.
N is INTEGER
The number of columns of the matrix A. N >= 0.
KL is INTEGER
The number of subdiagonals within the band of A. KL >= 0.
KU is INTEGER
The number of superdiagonals within the band of A. KU >= 0.
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(N,j+kl)
LDAB is INTEGER
The leading dimension of the array A. LDAB >= max(1,M).
R is REAL array, dimension (M)
If INFO = 0 or INFO > M, R contains the row scale factors
C is REAL array, dimension (N)
If INFO = 0, C contains the column scale factors for A.
ROWCND is REAL
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 is REAL
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 is REAL
Absolute value of largest matrix element. If AMAX is very
close to overflow or very close to underflow, the matrix
should be scaled.
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: if INFO = i, and i is
<= M: the i-th row of A is exactly zero
> M: the (i-M)-th column of A is exactly zero
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
Definition at line 160 of file sgbequb.f.
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.1 Sun May 26 2013 sgbequb.f(3)