NAG Library Routine Document

F06EGF (DSWAP)

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     N – INTEGERInput

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

2:     X($*$) – REAL (KIND=nag_wp) arrayInput/Output

Note: the dimension 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 $\mathbf{X}\left(1+\left(\mathit{i}-1\right)\times \mathbf{INCX}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{N}$.

If $\mathbf{INCX}<0$, $x_{\mathit{i}}$ must be stored in $\mathbf{X}\left(1-\left(\mathbf{N}-\mathit{i}\right)\times \mathbf{INCX}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{N}$.

Intermediate elements of X are not referenced.

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

Intermediate elements of X are unchanged.

3:     INCX – INTEGERInput

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

4:     Y($*$) – REAL (KIND=nag_wp) arrayInput/Output

Note: the dimension 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 original vector $x$ stored in the array elements used to supply the original vector $y$.

Intermediate elements of Y are unchanged.

5:     INCY – INTEGERInput

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

6  Error Indicators and Warnings

7  Accuracy

8  Further Comments

9  Example