NAG Library Routine Document

f06eaf  (ddot)

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1
Purpose

f06eaf (ddot) computes the scalar product of two real vectors.

2
Specification

Fortran Interface
Function f06eaf ( n, x, incx, y, incy)
Real (Kind=nag_wp):: f06eaf
Integer, Intent (In):: n, incx, incy
Real (Kind=nag_wp), Intent (In):: x(*), y(*)
C Header Interface
#include nagmk26.h
double  f06eaf_ ( const Integer *n, const double x[], const Integer *incx, const double y[], const Integer *incy)
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
Arguments

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 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
Parallelism and Performance

f06eaf (ddot) is not threaded in any implementation.

9
Further Comments

None.

10
Example

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