drotmg

DROTMG(1)                        BLAS routine                        DROTMG(1)



NAME
       DROTMG - CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH
       ZEROS  THE SECOND COMPONENT OF THE 2-VECTOR (DSQRT(DD1)*DX1,DSQRT(DD2)*

SYNOPSIS
       SUBROUTINE DROTMG(DD1,DD2,DX1,DY1,DPARAM)

           DOUBLE                                PRECISION DD1,DD2,DX1,DY1

           DOUBLE                                PRECISION DPARAM(5)

PURPOSE
          CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
          THE SECOND COMPONENT OF THE 2-VECTOR  (DSQRT(DD1)*DX1,DSQRT(DD2)*
          DY2)**T.
          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).
          LOCATIONS 2-4 OF DPARAM CONTAIN DH11, DH21, DH12, AND DH22
          RESPECTIVELY. (VALUES OF 1.D0, -1.D0, OR 0.D0 IMPLIED BY THE
          VALUE OF DPARAM(1) ARE NOT STORED IN DPARAM.)

          THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
          INEXACT.  THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
          OF DD1 AND DD2.  ALL ACTUAL SCALING OF DATA IS DONE USING GAM.



ARGUMENTS
       DD1    (input/output) DOUBLE PRECISION

       DD2    (input/output) DOUBLE PRECISION

       DX1    (input/output) DOUBLE PRECISION

       DY1    (input) DOUBLE PRECISION

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



BLAS routine                     November 2008                       DROTMG(1)