F06EAF (DDOT) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F06EAF (DDOT)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

+ Contents

    1  Purpose
    7  Accuracy
    9  Example

1  Purpose

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

2  Specification

FUNCTION F06EAF ( N, X, INCX, Y, INCY)
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.

3  Description

F06EAF (DDOT) returns, via the function name, the value of the scalar product
xTy
where x and y are n-element real vectors scattered with stride
INCX and INCY respectively.

4  References

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

5  Parameters

1:     N – INTEGERInput
2:     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.
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 max1, 1+N-1 ×INCY .
On entry: the n-element vector y.
If INCY>0, yi must be stored in Y1+i-1×INCY, for i=1,2,,N.
If INCY<0, yi must be stored in Y1-N-i×INCY, for i=1,2,,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.

6  Error Indicators and Warnings

None.

7  Accuracy

Not applicable.

8  Further Comments

None.

9  Example

None.

F06EAF (DDOT) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012