NAG FL Interface
f06etf (daxpyi)

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1 Purpose

f06etf adds a scaled sparse real vector, stored in compressed form, to an unscaled real vector.

2 Specification

Fortran Interface
Subroutine f06etf ( nz, a, x, indx, y)
Integer, Intent (In) :: nz, indx(*)
Real (Kind=nag_wp), Intent (In) :: a, x(*)
Real (Kind=nag_wp), Intent (Inout) :: y(*)
C Header Interface
#include <nag.h>
void  f06etf_ (const Integer *nz, const double *a, const double x[], const Integer indx[], double y[])
The routine may be called by the names f06etf, nagf_blas_daxpyi or its BLAS name daxpyi.

3 Description

f06etf performs the operation
yαx+y  
where x is a sparse real vector, stored in compressed form, and y is a real vector in full storage 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 sparse vector x.
2: a Real (Kind=nag_wp) Input
On entry: the scalar α.
3: x(*) Real (Kind=nag_wp) array Input
Note: the dimension of the array x must be at least max(1,nz) .
On entry: the nonzero elements of the sparse 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 of x(i) in the sparse vector x, for i=1,2,,nz.
Constraint: the indices must be distinct.
5: y(*) Real (Kind=nag_wp) array Input/Output
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.
On exit: the updated vector y.

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
f06etf is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.