NAG Library Routine Document

f06euf (dgthr)

1
Purpose

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

2
Specification

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(*)
C Header Interface
#include <nagmk26.h>
void  f06euf_ (const Integer *nz, const double y[], double x[], const Integer indx[])
The routine may be called by its BLAS name dgthr.

3
Description

f06euf (dgthr) gathers the specified elements of a vector, y, in full storage form, into x, the equivalent sparse vector compressed form.

4
References

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

5
Arguments

1:     nz – IntegerInput
On entry: the number of nonzeros in the compressed sparse vector x.
2:     y* – Real (Kind=nag_wp) arrayInput
Note: the dimension of the array y must be at least maxkindxk .
On entry: the vector y. Only elements corresponding to indices in indx are accessed.
3:     x* – Real (Kind=nag_wp) arrayOutput
Note: the dimension of the array x must be at least max1,nz.
On exit: the compressed vector x.
4:     indx* – Integer arrayInput
Note: the dimension of the array indx must be at least max1,nz .
On entry: indxi must contain the index yi, for i=1,2,,nz, which is to be gathered into x.

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06euf (dgthr) is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.