HP MLIB User's Guide Vol. 1 7th Ed.

118 HP MLIB User’s Guide

SROTG/DROTG/CROTG/ZROTG Construct Givens rotation

Name SROTG/DROTG/CROTG/ZROTG

Construct Givens rotation

Purpose Given real or complex scalars a and b, these subprograms construct a Givens

plane rotation matrix that annihilates b. Speciﬁcally, they determine scalars c

and s such that

where c is real, r and s are of the same type as a and b, and is the complex

conjugate of s.

Usually, c and s are passed to companion subprogram SROT, DROT, CROT, or

ZROT to apply the Givens rotation to a pair of vectors.

SROTG and DROTG also determine a quantity z that permits the later stable

reconstruction of c and s from a single quantity.

Usage VECLIB, VECLIB8:

REAL*4 a, b, c, s

CALL SROTG(a, b, c, s)

REAL*8 a, b, c, s

CALL DROTG(a, b, c, s)

REAL*4 c

COMPLEX*8 a, b, s

CALL CROTG(a, b, c, s)

REAL*8 c

COMPLEX*16 a, b, s

CALL ZROTG(a, b, c, s)

Input a The scalar a.

b The scalar b.

s– c

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