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