NAME¶

DROTM - APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX (DX**T) , WHERE **T INDICATES TRANSPOSE

SYNOPSIS¶

SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)

INTEGER INCX,INCY,N DOUBLE PRECISION DPARAM(5),DX(1),DY(1)

PURPOSE¶

APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
(DY**T)

DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..

DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0

(DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
H=( ) ( ) ( ) ( )
(DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.

ARGUMENTS¶

N (input) INTEGER

number of elements in input vector(s)

DX (input/output) DOUBLE PRECISION array, dimension N

double precision vector with 5 elements

INCX (input) INTEGER

storage spacing between elements of DX

DY (input/output) DOUBLE PRECISION array, dimension N

double precision vector with N elements

INCY (input) INTEGER

storage spacing between elements of DY

DPARAM (input/output) DOUBLE PRECISION array, dimension 5 DPARAM(1)=DFLAG DPARAM(2)=DH11 DPARAM(3)=DH21 DPARAM(4)=DH12 DPARAM(5)=DH22