NAG FL Interface
f06fkf (dnrm2w)

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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 <nag.h>
double  f06fkf_ (const Integer *n, const double w[], const Integer *incw, const double x[], const Integer *incx)
The routine may be called by the names f06fkf or nagf_blas_dnrm2w.

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=diag(w) and w is a vector of weights scattered with stride incw.

4 References

None.

5 Arguments

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

Background information to multithreading can be found in the Multithreading documentation.
f06fkf is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.