NAG Library Function Document

nag_daxpby (f16ecc)

1  Purpose

2  Specification

3  Description

4  References

5  Arguments

1:     n – IntegerInput

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

Constraint: $\mathbf{n}\ge 0$.

2:     alpha – doubleInput

On entry: the scalar $\alpha$.

3:     x[$\mathit{dim}$] – const doubleInput

Note: the dimension, dim, of the array x must be at least $\max \left(1,1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right)$.

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

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

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

Intermediate elements of x are not referenced.

4:     incx – IntegerInput

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

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

5:     beta – doubleInput

On entry: the scalar $\beta$.

6:     y[$\mathit{dim}$] – const doubleInput

Note: the dimension, dim, of the array y must be at least $\max \left(1,1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incy}\right|\right)$.

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

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

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

Intermediate elements of y are not referenced.

On exit: the updated vector $y$ stored in the array elements used to supply the original vector $y$.

Intermediate elements of y are unchanged.

7:     incy – IntegerInput

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

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

8:     fail – NagError *Input/Output

The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

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

On entry, $\mathbf{n}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{n}\ge 0$.

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example

10.1  Program Text

Program Text (f16ecce.c)

10.2  Program Data

Program Data (f16ecce.d)

10.3  Program Results

Program Results (f16ecce.r)