F06EXF (DROTI) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F06EXF (DROTI)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

+ Contents

    1  Purpose
    7  Accuracy
    9  Example

1  Purpose

F06EXF (DROTI) applies a real plane rotation to a sparse real vector and a real vector.

2  Specification

SUBROUTINE F06EXF ( NZ, X, INDX, Y, C, S)
INTEGER  NZ, INDX(*)
REAL (KIND=nag_wp)  X(*), Y(*), C, 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  Parameters

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  Further Comments

None.

9  Example

None.

F06EXF (DROTI) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012