NAG Library Routine Document

F06ETF (DAXPYI)

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     $\mathrm{NZ}$ – INTEGERInput

On entry: the number of nonzeros in the sparse vector $x$.

2:     $\mathrm{A}$ – REAL (KIND=nag_wp)Input

On entry: the scalar $\alpha$.

3:     $\mathrm{X}\left(*\right)$ – REAL (KIND=nag_wp) arrayInput

Note: the dimension of the array X must be at least $\max \left(1,\mathbf{NZ}\right)$.

On entry: the nonzero elements of the sparse vector $x$.

4:     $\mathrm{INDX}\left(*\right)$ – INTEGER arrayInput

Note: the dimension of the array INDX must be at least $\max \left(1,\mathbf{NZ}\right)$.

On entry: $\mathbf{INDX}\left(\mathit{i}\right)$ must contain the index of $\mathbf{X}\left(\mathit{i}\right)$ in the sparse vector $x$, for $\mathit{i}=1,2,\dots ,\mathbf{NZ}$.

Constraint: the indices must be distinct.

5:     $\mathrm{Y}\left(*\right)$ – REAL (KIND=nag_wp) arrayInput/Output

Note: the dimension of the array Y must be at least ${\displaystyle \underset{\mathit{k}}{\max }}\left\{\mathbf{INDX}\left(\mathit{k}\right)\right\}$.

On entry: the vector $y$. Only elements corresponding to indices in INDX are accessed.

On exit: the updated vector $y$.

6  Error Indicators and Warnings

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example