# NAG Library Routine Document

## 1Purpose

f06ewf (dsctr) scatters the elements of a sparse real vector $x$ stored in compressed form, into a real vector $y$ in full storage form.

## 2Specification

Fortran Interface
 Subroutine f06ewf ( nz, x, indx, y)
 Integer, Intent (In) :: nz, indx(*) Real (Kind=nag_wp), Intent (In) :: x(*) Real (Kind=nag_wp), Intent (Inout) :: y(*)
#include <nagmk26.h>
 void f06ewf_ (const Integer *nz, const double x[], const Integer indx[], double y[])
The routine may be called by its BLAS name dsctr.

## 3Description

f06ewf (dsctr) scatters the elements of a vector $x$, stored in compressed form, into a vector, $y$, in full storage form.

## 4References

Dodson D S, Grimes R G and Lewis J G (1991) Sparse extensions to the Fortran basic linear algebra subprograms ACM Trans. Math. Software 17 253–263

## 5Arguments

1:     $\mathbf{nz}$ – IntegerInput
On entry: the number of nonzeros in the sparse vector $x$.
2:     $\mathbf{x}\left(*\right)$ – Real (Kind=nag_wp) arrayInput
Note: the dimension of the array x must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{nz}}\right)$.
On entry: the nonzero elements of the sparse vector $x$.
3:     $\mathbf{indx}\left(*\right)$ – Integer arrayInput
Note: the dimension of the array indx must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{nz}}\right)$.
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.
4:     $\mathbf{y}\left(*\right)$ – Real (Kind=nag_wp) arrayInput/Output
Note: the dimension of the array y must be at least $\underset{\mathit{k}}{\mathrm{max}}\phantom{\rule{0.25em}{0ex}}\left\{{\mathbf{indx}}\left(\mathit{k}\right)\right\}$.
On entry: the vector $y$.
On exit: the vector $y$, with the elements corresponding to indices in indx altered.

None.

Not applicable.

## 8Parallelism and Performance

f06ewf (dsctr) is not threaded in any implementation.