NAG Library Routine Document

f06fkf  (dnrm2w)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:     $\mathbf{n}$ – IntegerInput

On entry: $n$, the number of elements in $x$.

2:     $\mathbf{w}\left(*\right)$ – Real (Kind=nag_wp) arrayInput

Note: the dimension of the array w must be at least $\max \left(1,1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incw}\right|\right)$.

On entry: $w$, the vector of weights.

If $\mathbf{incw}>0$, $w_{\mathit{i}}$ must be stored in $\mathbf{w}\left(1+\left(\mathit{i}-1\right)\times \mathbf{incx}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incw}<0$, $w_{\mathit{i}}$ must be stored in $\mathbf{w}\left(1-\left(\mathbf{n}-\mathit{i}\right)\times \mathbf{incw}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Constraint: All weights must be non-negative.

3:     $\mathbf{incw}$ – IntegerInput

On entry: the increment in the subscripts of w between successive elements of $w$.

4:     $\mathbf{x}\left(*\right)$ – Real (Kind=nag_wp) arrayInput

Note: the dimension of the array x must be at least $\max \left(1,1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right)$.

On entry: the $n$-element vector $x$.

If $\mathbf{incx}>0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(1+\left(\mathit{i}-1\right)\times \mathbf{incx}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incx}<0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(1-\left(\mathbf{n}-\mathit{i}\right)\times \mathbf{incx}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of x are not referenced.

5:     $\mathbf{incx}$ – IntegerInput

On entry: the increment in the subscripts of x between successive elements of $x$.

6

Error Indicators and Warnings

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Accuracy

8

Parallelism and Performance

9

Further Comments

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Example