NAG FL Interface
f06rbf (dlangb)

Settings help

FL Name Style:

FL Specification Language:

1 Purpose

f06rbf returns, via the function name, the value of the 1-norm, the -norm, the Frobenius norm, or the maximum absolute value of the elements of a real n×n band matrix.

2 Specification

Fortran Interface
Function f06rbf ( norm, n, kl, ku, ab, ldab, work)
Real (Kind=nag_wp) :: f06rbf
Integer, Intent (In) :: n, kl, ku, ldab
Real (Kind=nag_wp), Intent (In) :: ab(ldab,*)
Real (Kind=nag_wp), Intent (Inout) :: work(*)
Character (1), Intent (In) :: norm
C Header Interface
#include <nag.h>
double  f06rbf_ (const char *norm, const Integer *n, const Integer *kl, const Integer *ku, const double ab[], const Integer *ldab, double work[], const Charlen length_norm)
The routine may be called by the names f06rbf or nagf_blas_dlangb.

3 Description


4 References


5 Arguments

1: norm Character(1) Input
On entry: specifies the value to be returned.
norm='1' or 'O'
The 1-norm.
The -norm.
norm='F' or 'E'
The Frobenius (or Euclidean) norm.
The value maxi,j|aij| (not a norm).
Constraint: norm='1', 'O', 'I', 'F', 'E' or 'M'.
2: n Integer Input
On entry: n, the order of the matrix A.
When n=0, f06rbf returns zero.
Constraint: n0.
3: kl Integer Input
On entry: kl, the number of subdiagonals within the band of A.
Constraint: kl0.
4: ku Integer Input
On entry: ku, the number of superdiagonals within the band of A.
Constraint: ku0.
5: ab(ldab,*) Real (Kind=nag_wp) array Input
Note: the second dimension of the array ab must be at least n.
On entry: the n×n band matrix A.
The matrix is stored in rows 1 to kl+ku+1, more precisely, the element Aij must be stored in
ab(ku+1+i-j,j)  for ​max(1,j-ku)imin(n,j+kl).  
6: ldab Integer Input
On entry: the first dimension of the array ab as declared in the (sub)program from which f06rbf is called.
Constraint: ldabkl+ku+1.
7: work(*) Real (Kind=nag_wp) array Workspace
Note: the dimension of the array work must be at least max(1,n) if norm='I', and at least 1 otherwise.

6 Error Indicators and Warnings


7 Accuracy

Not applicable.

8 Parallelism and Performance

f06rbf is not threaded in any implementation.

9 Further Comments


10 Example