NAG Library Routine Document

f06fjf  (dssq)

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Purpose

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Specification

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Description

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References

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Arguments

1:     $\mathbf{n}$ – IntegerInput

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

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

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

On entry: the $n$-element vector $x$. $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(1+\left(\mathit{i}-1\right)\times \mathbf{incx}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of x are not referenced.

3:     $\mathbf{incx}$ – IntegerInput

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

Constraint: $\mathbf{incx}>0$.

4:     $\mathbf{scal}$ – Real (Kind=nag_wp)Input/Output

On entry: the scaling factor $\alpha$. On the first call to f06fjf $\mathbf{scal}=0.0$.

Constraint: $\mathbf{scal}\ge 0.0$.

On exit: the updated scaling factor $\tilde{\alpha }={\displaystyle \underset{i}{\max }}\left(\alpha ,\left|x_i\right|\right)$.

5:     $\mathbf{sumsq}$ – Real (Kind=nag_wp)Input/Output

On entry: the scaled sum of squares $\xi$. On the first call to f06fjf $\mathbf{sumsq}=1.0$.

Constraint: $\mathbf{sumsq}\ge 1.0$.

On exit: the updated scaled sum of squares $\tilde{\xi }$, satisfying: $1\le \tilde{\xi }\le \xi +n$.

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Error Indicators and Warnings

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Accuracy

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Parallelism and Performance

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Further Comments

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Example