# NAG Library Routine Document

## 1Purpose

f06fgf negates a real vector.

## 2Specification

Fortran Interface
 Subroutine f06fgf ( n, x, incx)
 Integer, Intent (In) :: n, incx Real (Kind=nag_wp), Intent (Inout) :: x(*)
#include nagmk26.h
 void f06fgf_ (const Integer *n, double x[], const Integer *incx)

## 3Description

f06fgf performs the operation
 $x←-x$
where $x$ is an $n$-element real vector scattered with stride incx.

None.

## 5Arguments

1:     $\mathbf{n}$ – IntegerInput
On entry: $n$, the number of elements in $x$.
2:     $\mathbf{x}\left(*\right)$ – Real (Kind=nag_wp) arrayInput/Output
Note: the dimension of the array x must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{n}}-1\right)×{\mathbf{incx}}\right)$.
On entry: the $n$-element vector $x$. ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left(1+\left(\mathit{i}-1\right)×{\mathbf{incx}}\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
Intermediate elements of x are not referenced.
On exit: the vector $-x$ stored in the array elements used to supply the original vector $x$.
Intermediate elements of x are unchanged.
3:     $\mathbf{incx}$ – IntegerInput
On entry: the increment in the subscripts of x between successive elements of $x$.
Constraint: ${\mathbf{incx}}>0$.

None.

Not applicable.

## 8Parallelism and Performance

f06fgf is not threaded in any implementation.