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

Chapter 2 Basic Vector Operations 129
Construct modified Givens rotation SROTMG/DROTMG
For each of the four values of param(1), only the
indicated values of param(2) through param(5) are
defined. The 0, 1, and −1 elements are not stored in
param.
Notes VECLIB also contains subprograms that construct and apply ordinary Givens
rotations. They are documented elsewhere in this chapter. The modified Givens
subprograms are a little more difficult to use but are more efficient.
Example Construct a modified Givens plane rotation that rotates vectors d
1
x and d
2
y in
such a way as to annihilate d
2
y
1
. x and y are vectors 10 elements long stored in
one-dimensional arrays X and Y of dimension 20.
REAL*8 D1,D2,X(20),Y(20),PARAM(5)
CALL DROTMG (D1,D2,X(1),Y(1),PARAM)
X(1) is the rotated result, so it should not be rotated by a subsequent call to
DROTM.
param 1() 1= H
param 2() 1
1– param 5()
=