# NAG FL Interfacef06euf (dgthr)

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## 1Purpose

f06euf gathers specified (usually nonzero) elements of a real vector $y$ in full storage form into a sparse real vector $x$ in compressed form.

## 2Specification

Fortran Interface
 Subroutine f06euf ( nz, y, x, indx)
 Integer, Intent (In) :: nz, indx(*) Real (Kind=nag_wp), Intent (In) :: y(*) Real (Kind=nag_wp), Intent (Inout) :: x(*)
#include <nag.h>
 void f06euf_ (const Integer *nz, const double y[], double x[], const Integer indx[])
The routine may be called by the names f06euf, nagf_blas_dgthr or its BLAS name dgthr.

## 3Description

f06euf gathers the specified elements of a vector, $y$, in full storage form, into $x$, the equivalent sparse vector compressed 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: $\mathbf{nz}$Integer Input
On entry: the number of nonzeros in the compressed sparse vector $x$.
2: $\mathbf{y}\left(*\right)$Real (Kind=nag_wp) array Input
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 $y$. Only elements corresponding to indices in indx are accessed.
3: $\mathbf{x}\left(*\right)$Real (Kind=nag_wp) array Output
Note: the dimension of the array x must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,{\mathbf{nz}}\right)$.
On exit: the compressed vector $x$.
4: $\mathbf{indx}\left(*\right)$Integer array Input
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 ${\mathbf{y}}\left(\mathit{i}\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{nz}}$, which is to be gathered into $x$.

None.

Not applicable.