# drotm.f

          SUBROUTINE DROTM (N, DX, INCX, DY, INCY, DPARAM)
    C***BEGIN PROLOGUE  DROTM
    C***PURPOSE  Apply a modified Givens transformation.
    C***LIBRARY   SLATEC (BLAS)
    C***CATEGORY  D1A8
    C***TYPE      DOUBLE PRECISION (SROTM-S, DROTM-D)
    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***DESCRIPTION
    C
    C                B L A S  Subprogram
    C    Description of Parameters
    C
    C     --Input--
    C        N  number of elements in input vector(s)
    C       DX  double precision vector with N elements
    C     INCX  storage spacing between elements of DX
    C       DY  double precision vector with N elements
    C     INCY  storage spacing between elements of DY
    C   DPARAM  5-element D.P. vector.  DPARAM(1) is DFLAG described below.
    C           Locations 2-5 of SPARAM contain elements of the
    C           transformation matrix H described below.
    C
    C     --Output--
    C       DX  rotated vector (unchanged if N .LE. 0)
    C       DY  rotated vector (unchanged if N .LE. 0)
    C
    C     Apply the modified Givens transformation, H, to the 2 by N matrix
    C     (DX**T)
    C     (DY**T) , where **T indicates transpose.  The elements of DX are
    C     in DX(LX+I*INCX), I = 0 to N-1, where LX = 1 if INCX .GE. 0, else
    C     LX = 1+(1-N)*INCX, and similarly for DY using LY and INCY.
    C
    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     See DROTMG for a description of data storage in DPARAM.
    C
    C***REFERENCES  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
    C                 Krogh, Basic linear algebra subprograms for Fortran
    C                 usage, Algorithm No. 539, Transactions on Mathematical
    C                 Software 5, 3 (September 1979), pp. 308-323.
    C***ROUTINES CALLED  (NONE)
    C***REVISION HISTORY  (YYMMDD)
    C   791001  DATE WRITTEN
    C   861211  REVISION DATE from Version 3.2
    C   891214  Prologue converted to Version 4.0 format.  (BAB)
    C   920310  Corrected definition of LX in DESCRIPTION.  (WRB)
    C   920501  Reformatted the REFERENCES section.  (WRB)
    C***END PROLOGUE  DROTM