NAG Library Routine Document

f06etf (daxpyi)

1
Purpose

f06etf (daxpyi) 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 <nagmk26.h>
void  f06etf_ (const Integer *nz, const double *a, const double x[], const Integer indx[], double y[])
The routine may be called by its BLAS name daxpyi.

3
Description

f06etf (daxpyi) 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 – IntegerInput
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) arrayInput
Note: the dimension of the array x must be at least max1,nz .
On entry: the nonzero elements of the sparse 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 of xi in the sparse vector x, for i=1,2,,nz.
Constraint: the indices must be distinct.
5:     y* – Real (Kind=nag_wp) arrayInput/Output
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.
On exit: the updated vector y.

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06etf (daxpyi) is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.