F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentF06KLF

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

## 1  Purpose

F06KLF determines the index of the first negligible element of a real vector.

## 2  Specification

 FUNCTION F06KLF ( N, X, INCX, TOL)
 INTEGER F06KLF
 INTEGER N, INCX REAL (KIND=nag_wp) X(*), TOL

## 3  Description

F06KLF finds the first element of the $n$-element real vector $x$ for which
 $xk+1≤tolmaxx1,…,xk$
and returns the index $k$ via the function name. If no such $k$ exists, then the value $n$ is returned. If a negative value of $\mathit{tol}$ is supplied, the value of machine precision is used in place of $\mathit{tol}$.

None.

## 5  Parameters

1:     N – INTEGERInput
On entry: $n$, the number of elements in $x$.
2:     X($*$) – REAL (KIND=nag_wp) arrayInput
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.
3:     INCX – INTEGERInput
On entry: the increment in the subscripts of X between successive elements of $x$.
Constraint: ${\mathbf{INCX}}>0$.
4:     TOL – REAL (KIND=nag_wp)Input
On entry: the value $\mathit{tol}$.

None.

Not applicable.