NAG C Library Function Document

nag_ddot (f16eac)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:    $\mathbf{conj}$ – Nag_ConjTypeInput

On entry: conj is not used. The presence of this argument in the BLAST standard is for consistency with the interface of the complex variant of this function.

Constraint: $\mathbf{conj}=\mathrm{Nag\_NoConj}$ or $\mathrm{Nag\_Conj}$.

2:    $\mathbf{n}$ – IntegerInput

On entry: $n$, the number of elements in $x$ and $y$.

3:    $\mathbf{alpha}$ – doubleInput

On entry: the scalar $\alpha$.

4:    $\mathbf{x}\left[1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right]$ – const doubleInput

On entry: the $n$-element vector $x$.

If $\mathbf{incx}>0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left[\left(\mathit{i}-1\right)\times \mathbf{incx}\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incx}<0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left[\left(\mathbf{n}-\mathit{i}\right)\times \left|\mathbf{incx}\right|\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of x are not referenced. If $\alpha =0.0$ or $\mathbf{n}=0$, x is not referenced and may be NULL.

5:    $\mathbf{incx}$ – IntegerInput

On entry: the increment in the subscripts of x between successive elements of $x$.

Constraint: $\mathbf{incx}\ne 0$.

6:    $\mathbf{beta}$ – doubleInput

On entry: the scalar $\beta$.

7:    $\mathbf{y}\left[1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incy}\right|\right]$ – const doubleInput

On entry: the $n$-element vector $y$.

If $\mathbf{incy}>0$, $y_{\mathit{i}}$ must be stored in $\mathbf{y}\left[\left(\mathit{i}-1\right)\times \mathbf{incy}\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incy}<0$, $y_{\mathit{i}}$ must be stored in $\mathbf{y}\left[\left(\mathbf{n}-\mathit{i}\right)\times \left|\mathbf{incy}\right|\right]$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of y are not referenced. If $\alpha =0.0$ or $\mathbf{n}=0$, y is not referenced and may be NULL.

8:    $\mathbf{incy}$ – IntegerInput

On entry: the increment in the subscripts of y between successive elements of $y$.

Constraint: $\mathbf{incy}\ne 0$.

9:    $\mathbf{r}$ – double *Input/Output

On entry: the initial value, $r$, to be updated. If $\beta =0.0$, r need not be set on entry.

On exit: the value $r$, scaled by $\beta$ and updated by the scaled dot product of $x$ and $y$.

10:  $\mathbf{fail}$ – NagError *Input/Output

The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6

Error Indicators and Warnings

NE_ALLOC_FAIL

Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.

NE_BAD_PARAM

On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.

NE_INT

On entry, $\mathbf{incx}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{incx}\ne 0$.

On entry, $\mathbf{incy}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{incy}\ne 0$.

NE_NO_LICENCE

Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

Program Text (f16eace.c)

10.2

Program Data

Program Data (f16eace.d)

10.3

Program Results

Program Results (f16eace.r)