NAG Library Routine Document

F06EAF (DDOT)

+− Contents

1 Purpose

9 Example

F06EAF (DDOT) computes the scalar product of two real vectors.

FUNCTION F06EAF (

REAL (KIND=nag_wp) F06EAF

INTEGER	N, INCX, INCY
REAL (KIND=nag_wp)	X(), Y()

The routine may be called by its BLAS name ddot.

F06EAF (DDOT) returns, via the function name, the value of the scalar product

x^{T} y

where

x

and

y

are

n

-element real vectors scattered with stride INCX and INCY respectively.

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 $x$ and $y$ .
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 $x$ .
If $INCX > 0$ , $x_{i}$ must be stored in $X (1 + (i - 1) \times INCX)$ , for $i = 1, 2, \dots, N$ .

If $INCX < 0$ , $x_{i}$ must be stored in $X (1 - (N - i) \times INCX)$ , 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 $x$ .
4: Y( $*$ ) – REAL (KIND=nag_wp) arrayInput: Note: the dimension of the array Y must be at least $\max (1, 1 + (N - 1) \times |INCY|)$ .
On entry: the $n$ -element vector $y$ .
If $INCY > 0$ , $y_{i}$ must be stored in $Y (1 + (i - 1) \times INCY)$ , for $i = 1, 2, \dots, N$ .

If $INCY < 0$ , $y_{i}$ must be stored in $Y (1 - (N - i) \times INCY)$ , for $i = 1, 2, \dots, N$ .

Intermediate elements of Y are not referenced.
5: INCY – INTEGERInput: On entry: the increment in the subscripts of Y between successive elements of $y$ .