NAG FL Interface
f06exf (droti)

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1 Purpose

f06exf applies a real plane rotation to a sparse real vector and a real vector.

2 Specification

Fortran Interface
Subroutine f06exf ( nz, x, indx, y, c, s)
Integer, Intent (In) :: nz, indx(*)
Real (Kind=nag_wp), Intent (In) :: c, s
Real (Kind=nag_wp), Intent (Inout) :: x(*), y(*)
C Header Interface
#include <nag.h>
void  f06exf_ (const Integer *nz, double x[], const Integer indx[], double y[], const double *c, const double *s)
The routine may be called by the names f06exf, nagf_blas_droti or its BLAS name droti.

3 Description

f06exf applies a real plane rotation to a sparse real vector x stored in compressed form and a real vector y in full storage form:
( xT yT ) ( c s -s c ) ( xT yT ) .  
The plane rotation has the form generated by f06aaf or f06baf.

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: x(*) Real (Kind=nag_wp) array Input/Output
Note: the dimension of the array x must be at least max(1,nz) .
On entry: the nonzero elements of the sparse vector x.
On exit: the transformed vector x.
3: 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.
4: 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 the elements corresponding to indices in indx are referenced.
On exit: the transformed vector y. Only elements corresponding to indices in indx are altered.
5: c Real (Kind=nag_wp) Input
On entry: the value c, the cosine of the rotation.
6: s Real (Kind=nag_wp) Input
On entry: the value s, the sine of the rotation.

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

f06exf is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.