NAG Library Routine Document

F06FJF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     $\mathrm{N}$ – INTEGERInput

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

2:     $\mathrm{X}\left(*\right)$ – 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:     $\mathrm{INCX}$ – INTEGERInput

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

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

4:     $\mathrm{SCAL}$ – 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:     $\mathrm{SUMSQ}$ – 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: $1\le \tilde{\xi }\le \xi +n$.

6  Error Indicators and Warnings

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example