NAG Library Routine Document

f06fkf  (dnrm2w)

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1
Purpose

f06fkf computes the weighted Euclidean norm of a real vector.

2
Specification

Fortran Interface
Function f06fkf ( n, w, incw, x, incx)
Real (Kind=nag_wp):: f06fkf
Integer, Intent (In):: n, incw, incx
Real (Kind=nag_wp), Intent (In):: w(*), x(*)
C Header Interface
#include nagmk26.h
double  f06fkf_ ( const Integer *n, const double w[], const Integer *incw, const double x[], const Integer *incx)

3
Description

f06fkf returns, via the function name, the weighted Euclidean norm
xTWx  
of the n-element real vector x scattered with stride incw and incx respectively, where W=diagw and w is a vector of weights scattered with stride incw.

4
References

None.

5
Arguments

1:     n – IntegerInput
On entry: n, the number of elements in x.
2:     w* – Real (Kind=nag_wp) arrayInput
Note: the dimension of the array w must be at least max1, 1+n-1 ×incw .
On entry: w, the vector of weights.
If incw>0, wi must be stored in w1+i-1×incx , for i=1,2,,n.
If incw<0, wi must be stored in w1-n-i×incw , for i=1,2,,n.
Constraint: All weights must be non-negative.
3:     incw – IntegerInput
On entry: the increment in the subscripts of w between successive elements of w.
4:     x* – Real (Kind=nag_wp) arrayInput
Note: the dimension of the array x must be at least max1, 1+n-1 ×incx .
On entry: the n-element vector x.
If incx>0, xi must be stored in x1+i-1×incx, for i=1,2,,n.
If incx<0, xi must be stored in x1-n-i×incx, for i=1,2,,n.
Intermediate elements of x are not referenced.
5:     incx – IntegerInput
On entry: the increment in the subscripts of x between successive elements of x.

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06fkf is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017