# srotmg.f

          SUBROUTINE SROTMG (SD1, SD2, SX1, SY1, SPARAM)
    C***BEGIN PROLOGUE  SROTMG
    C***PURPOSE  Construct a modified Givens transformation.
    C***LIBRARY   SLATEC (BLAS)
    C***CATEGORY  D1B10
    C***TYPE      SINGLE PRECISION (SROTMG-S, DROTMG-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      SD1  single precision scalar
    C      SD2  single precision scalar
    C      SX1  single precision scalar
    C      SY2  single precision scalar
    C   SPARAM  S.P. 5-vector. SPARAM(1)=SFLAG defined below.
    C           Locations 2-5 contain the rotation matrix.
    C
    C     --Output--
    C      SD1  changed to represent the effect of the transformation
    C      SD2  changed to represent the effect of the transformation
    C      SX1  changed to represent the effect of the transformation
    C      SY2  unchanged
    C
    C     Construct the modified Givens transformation matrix H which zeros
    C     the second component of the 2-vector  (SQRT(SD1)*SX1,SQRT(SD2)*
    C     SY2)**T.
    C     With SPARAM(1)=SFLAG, H has one of the following forms:
    C
    C     SFLAG=-1.E0     SFLAG=0.E0        SFLAG=1.E0     SFLAG=-2.E0
    C
    C       (SH11  SH12)    (1.E0  SH12)    (SH11  1.E0)    (1.E0  0.E0)
    C     H=(          )    (          )    (          )    (          )
    C       (SH21  SH22),   (SH21  1.E0),   (-1.E0 SH22),   (0.E0  1.E0).
    C
    C     Locations 2-5 of SPARAM contain SH11, SH21, SH12, and SH22,
    C     respectively.  (Values of 1.E0, -1.E0, or 0.E0 implied by the
    C     value of SPARAM(1) are not stored in SPARAM.)
    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   780301  DATE WRITTEN
    C   861211  REVISION DATE from Version 3.2
    C   891214  Prologue converted to Version 4.0 format.  (BAB)
    C   920316  Prologue corrected.  (WRB)
    C   920501  Reformatted the REFERENCES section.  (WRB)
    C***END PROLOGUE  SROTMG