NAG Library Routine Document

F06EJF (DNRM2)

+− Contents

1 Purpose

9 Example

F06EJF (DNRM2) returns the Euclidean norm of the

n

-element real vector

x

FUNCTION F06EJF (

REAL (KIND=nag_wp) F06EJF

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

The routine may be called by its BLAS name dnrm2.

F06EJF (DNRM2) returns, via the function name, the Euclidean norm

{‖x‖}_{2} = \sqrt{x^{T} x}

of the

n

-element real vector

x

scattered with stride INCX.

Lawson C L, Hanson R J, Kincaid D R and Krogh F T (1979) Basic linear algebra supbrograms for Fortran usage ACM Trans. Math. Software 5 308–325

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: $INCX > 0$ .