NAG FL Interface
f06euf (dgthr)

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FL Name Style:

FL Specification Language:

1 Purpose

f06euf 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 <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.

3 Description

f06euf 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 Integer Input
On entry: the number of nonzeros in the compressed sparse vector x.
2: y(*) Real (Kind=nag_wp) array Input
Note: the dimension of the array y must be at least maxk{indx(k)} .
On entry: the vector y. Only elements corresponding to indices in indx are accessed.
3: x(*) Real (Kind=nag_wp) array Output
Note: the dimension of the array x must be at least max(1,nz).
On exit: the compressed vector x.
4: indx(*) Integer array Input
Note: the dimension of the array indx must be at least max(1,nz) .
On entry: indx(i) must contain the index y(i), for i=1,2,,nz, which is to be gathered into x.

6 Error Indicators and Warnings


7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
f06euf is not threaded in any implementation.

9 Further Comments


10 Example