# doubleGBauxiliary - Man Page

double

## Synopsis

### Functions

double precision function dlangb (NORM, N, KL, KU, AB, LDAB, WORK)
DLANGB returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of general band matrix.
subroutine dlaqgb (M, N, KL, KU, AB, LDAB, R, C, ROWCND, COLCND, AMAX, EQUED)
DLAQGB scales a general band matrix, using row and column scaling factors computed by sgbequ.

## Detailed Description

This is the group of double auxiliary functions for GB matrices

## Function Documentation

### double precision function dlangb (character NORM, integer N, integer KL, integer KU, double precision, dimension( ldab, * ) AB, integer LDAB, double precision, dimension( * ) WORK)

DLANGB returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of general band matrix.

Purpose:

DLANGB  returns the value of the one norm,  or the Frobenius norm, or
the  infinity norm,  or the element of  largest absolute value  of an
n by n band matrix  A,  with kl sub-diagonals and ku super-diagonals.
Returns

DLANGB

DLANGB = ( max(abs(A(i,j))), NORM = 'M' or 'm'
(
( norm1(A),         NORM = '1', 'O' or 'o'
(
( normI(A),         NORM = 'I' or 'i'
(
( normF(A),         NORM = 'F', 'f', 'E' or 'e'

where  norm1  denotes the  one norm of a matrix (maximum column sum),
normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
normF  denotes the  Frobenius norm of a matrix (square root of sum of
squares).  Note that  max(abs(A(i,j)))  is not a consistent matrix norm.
Parameters

NORM

NORM is CHARACTER*1
Specifies the value to be returned in DLANGB as described
above.

N

N is INTEGER
The order of the matrix A.  N >= 0.  When N = 0, DLANGB is
set to zero.

KL

KL is INTEGER
The number of sub-diagonals of the matrix A.  KL >= 0.

KU

KU is INTEGER
The number of super-diagonals of the matrix A.  KU >= 0.

AB

AB is DOUBLE PRECISION array, dimension (LDAB,N)
The band matrix A, stored 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

LDAB is INTEGER
The leading dimension of the array AB.  LDAB >= KL+KU+1.

WORK

WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK)),
where LWORK >= N when NORM = 'I'; otherwise, WORK is not
referenced.
Author

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Definition at line 122 of file dlangb.f.

### 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.

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

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.

KL

KL is INTEGER
The number of subdiagonals within the band of A.  KL >= 0.

KU

KU is INTEGER
The number of superdiagonals within the band of A.  KU >= 0.

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.

LDAB

LDAB is INTEGER
The leading dimension of the array AB.  LDA >= KL+KU+1.

R

R is DOUBLE PRECISION array, dimension (M)
The row scale factors for A.

C

C is DOUBLE PRECISION array, dimension (N)
The column scale factors for A.

ROWCND

ROWCND is DOUBLE PRECISION
Ratio of the smallest R(i) to the largest R(i).

COLCND

COLCND is DOUBLE PRECISION
Ratio of the smallest C(i) to the largest C(i).

AMAX

AMAX is DOUBLE PRECISION
Absolute value of largest matrix entry.

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

NAG Ltd.

Definition at line 157 of file dlaqgb.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man pages dlangb(3) and dlaqgb(3) are aliases of doubleGBauxiliary(3).

Mon Jun 28 2021 Version 3.10.0 LAPACK