naginterfaces.library.blas.dlangb

naginterfaces.library.blas.dlangb(norm, kl, ku, ab)

dlangb returns the value of the $1$-norm, the $\infty$-norm, the Frobenius norm, or the maximum absolute value of the elements of a real $n\times n$ band matrix.

For full information please refer to the NAG Library document for f06rb

https://support.nag.com/numeric/nl/nagdoc_30.1/flhtml/f06/f06rbf.html

Parameters

normstr, length 1

Specifies the value to be returned.

$norm=\text{'1'}$ or $\text{'O'}$

The $1$-norm.

$norm=\text{'I'}$

The $\infty$-norm.

$norm=\text{'F'}$ or $\text{'E'}$

The Frobenius (or Euclidean) norm.

$norm=\text{'M'}$

The value ${max}_{i,j}\left(\left|a_{ij}\right|\right)$ (not a norm).

klint

$k_l$, the number of subdiagonals within the band of $A$.

kuint

$k_u$, the number of superdiagonals within the band of $A$.

abfloat, array-like, shape $(kl+ku+1,n)$

The $n\times n$ band matrix $A$.

Returns

nrmfloat

The value of the $1$-norm, the $\infty$-norm, the Frobenius norm, or the maximum absolute value of the elements of the real $n\times n$ band matrix.

Raises

NagValueError

(errno $1$)

On entry, error in parameter $norm$.

Constraint: $norm=\text{'1'}$, $\text{'O'}$, $\text{'I'}$, $\text{'F'}$, $\text{'E'}$ or $\text{'M'}$.

(errno $2$)

On entry, error in parameter $\text{n}$.

Constraint: $n\ge 0$.

(errno $3$)

On entry, error in parameter $kl$.

Constraint: $kl\ge 0$.

(errno $4$)

On entry, error in parameter $ku$.

Constraint: $ku\ge 0$.

Notes

No equivalent traditional C interface for this routine exists in the NAG Library.