NAG Library Routine Document

f06exf (droti)

1
Purpose

f06exf (droti) 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 <nagmk26.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 its BLAS name droti.

3
Description

f06exf (droti) 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 (drotg) 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 – IntegerInput
On entry: the number of nonzeros in the sparse vector x.
2:     x* – Real (Kind=nag_wp) arrayInput/Output
Note: the dimension of the array x must be at least max1,nz .
On entry: the nonzero elements of the sparse vector x.
On exit: the transformed vector x.
3:     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.
4:     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 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 (droti) is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.