SUBROUTINE DROTMG(DD1,DD2,DX1,DY1,DPARAM)
C***BEGIN PROLOGUE  DROTMG
C***DATE WRITTEN   780301   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  D1B10
C***KEYWORDS  BLAS,LINEAR ALGEBRA,MODIFIED GIVENS ROTATION,VECTOR
C***AUTHOR  LAWSON, C. L., (JPL)
C           HANSON, R. J., (SNLA)
C           KINCAID, D. R., (U. OF TEXAS)
C           KROGH, F. T., (JPL)
C***PURPOSE  Construct d.p. modified Givens transformation
C***DESCRIPTION
C
C                B L A S  Subprogram
C    Description of Parameters
C
C     --Input--
C      DD1  double precision scalar
C      DD2  double precision scalar
C      DX1  double precision scalar
C      DX2  double precision scalar
C   DPARAM  D.P. 5-vector. DPARAM(1)=DFLAG defined below.
C             Elements 2-5  define the transformation matrix H.
C
C     --Output--
C      DD1  changed to represent the effect of the transformation
C      DD2  changed to reflect the transformation
C      DX1  changed to reflect the transformation
C      DX2  unchanged
C
C     Construct the modified Givens transformation matrix H which zeros
C     the second component of the 2-vector  (DSQRT(DD1)*DX1,DSQRT(DD2)*
C     DY2)**T.
C     With DPARAM(1)=DFLAG, H has one of the following forms..
C
C     DFLAG=-1.D0     DFLAG=0.D0        DFLAG=1.D0     DFLAG=-2.D0
C
C       (DH11  DH12)    (1.D0  DH12)    (DH11  1.D0)    (1.D0  0.D0)
C     H=(          )    (          )    (          )    (          )
C       (DH21  DH22),   (DH21  1.D0),   (-1.D0 DH22),   (0.D0  1.D0).
C
C     Locations 2-5 of DPARAM contain DH11, DH21, DH12, and DH22
C     respectively.  (Values of 1.D0, -1.D0, or 0.D0 implied by the
C     value of DPARAM(1) are not stored in DPARAM.)
C***REFERENCES  LAWSON C.L., HANSON R.J., KINCAID D.R., KROGH F.T.,
C                 *BASIC LINEAR ALGEBRA SUBPROGRAMS FOR FORTRAN USAGE*,
C                 ALGORITHM NO. 539, TRANSACTIONS ON MATHEMATICAL
C                 SOFTWARE, VOLUME 5, NUMBER 3, SEPTEMBER 1979, 308-323
C***ROUTINES CALLED  (NONE)
C***END PROLOGUE  DROTMG