NAG Library Routine Document

F06KLF

+− Contents

1 Purpose

9 Example

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

FUNCTION F06KLF (

INTEGER F06KLF

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

F06KLF finds the first element of the

n

-element real vector

x

for which

|x_{k + 1}| \leq tol \max (|x_{1}|, \dots, |x_{k}|)

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

tol

is supplied, the value of machine precision is used in place of

tol

None.

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 $\max (1, 1 + (N - 1) \times INCX)$ .
On entry: the $n$ -element vector $x$ . $x_{i}$ must be stored in $X (1 + (i - 1) \times INCX)$ , for $i = 1, 2, \dots, N$ .
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: $INCX > 0$ .
4: TOL – REAL (KIND=nag_wp)Input: On entry: the value $tol$ .