naginterfaces.library.blas.dlangt

naginterfaces.library.blas.dlangt(norm, dl, d, du)

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

For full information please refer to the NAG Library document for f06rn

https://support.nag.com/numeric/nl/nagdoc_30.2/flhtml/f06/f06rnf.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).

dlfloat, array-like, shape $(n-1)$

The ($n-1$) subdiagonal elements of $A$.

dfloat, array-like, shape $\left(n\right)$

The $n$ diagonal elements of $A$.

dufloat, array-like, shape $(n-1)$

The ($n-1$) superdiagonal elements of $A$.

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 $n\times n$ tridiagonal matrix $A$.

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: $n\ge 0$.

Notes

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