numeric-linalg

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*> \brief \b SROTM
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       SUBROUTINE SROTM(N,SX,INCX,SY,INCY,SPARAM)
*
*       .. Scalar Arguments ..
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       REAL SPARAM(5),SX(*),SY(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
*>
*>    (SX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF SX ARE IN
*>    (SX**T)
*>
*>    SX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
*>    LX = (-INCX)*N, AND SIMILARLY FOR SY USING USING LY AND INCY.
*>    WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
*>
*>    SFLAG=-1.E0     SFLAG=0.E0        SFLAG=1.E0     SFLAG=-2.E0
*>
*>      (SH11  SH12)    (1.E0  SH12)    (SH11  1.E0)    (1.E0  0.E0)
*>    H=(          )    (          )    (          )    (          )
*>      (SH21  SH22),   (SH21  1.E0),   (-1.E0 SH22),   (0.E0  1.E0).
*>    SEE  SROTMG FOR A DESCRIPTION OF DATA STORAGE IN SPARAM.
*>
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in,out] SX
*> \verbatim
*>          SX is REAL array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>         storage spacing between elements of SX
*> \endverbatim
*>
*> \param[in,out] SY
*> \verbatim
*>          SY is REAL array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>         storage spacing between elements of SY
*> \endverbatim
*>
*> \param[in] SPARAM
*> \verbatim
*>          SPARAM is REAL array, dimension (5)
*>     SPARAM(1)=SFLAG
*>     SPARAM(2)=SH11
*>     SPARAM(3)=SH21
*>     SPARAM(4)=SH12
*>     SPARAM(5)=SH22
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup rotm
*
*  =====================================================================
      SUBROUTINE SROTM(N,SX,INCX,SY,INCY,SPARAM)
*
*  -- Reference BLAS level1 routine --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      REAL SPARAM(5),SX(*),SY(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      REAL SFLAG,SH11,SH12,SH21,SH22,TWO,W,Z,ZERO
      INTEGER I,KX,KY,NSTEPS
*     ..
*     .. Data statements ..
      DATA ZERO,TWO/0.E0,2.E0/
*     ..
*
      SFLAG = SPARAM(1)
      IF (N.LE.0 .OR. (SFLAG+TWO.EQ.ZERO)) RETURN
      IF (INCX.EQ.INCY.AND.INCX.GT.0) THEN
*
         NSTEPS = N*INCX
         IF (SFLAG.LT.ZERO) THEN
            SH11 = SPARAM(2)
            SH12 = SPARAM(4)
            SH21 = SPARAM(3)
            SH22 = SPARAM(5)
            DO I = 1,NSTEPS,INCX
               W = SX(I)
               Z = SY(I)
               SX(I) = W*SH11 + Z*SH12
               SY(I) = W*SH21 + Z*SH22
            END DO
         ELSE IF (SFLAG.EQ.ZERO) THEN
            SH12 = SPARAM(4)
            SH21 = SPARAM(3)
            DO I = 1,NSTEPS,INCX
               W = SX(I)
               Z = SY(I)
               SX(I) = W + Z*SH12
               SY(I) = W*SH21 + Z
            END DO
         ELSE
            SH11 = SPARAM(2)
            SH22 = SPARAM(5)
            DO I = 1,NSTEPS,INCX
               W = SX(I)
               Z = SY(I)
               SX(I) = W*SH11 + Z
               SY(I) = -W + SH22*Z
            END DO
         END IF
      ELSE
         KX = 1
         KY = 1
         IF (INCX.LT.0) KX = 1 + (1-N)*INCX
         IF (INCY.LT.0) KY = 1 + (1-N)*INCY
*
         IF (SFLAG.LT.ZERO) THEN
            SH11 = SPARAM(2)
            SH12 = SPARAM(4)
            SH21 = SPARAM(3)
            SH22 = SPARAM(5)
            DO I = 1,N
               W = SX(KX)
               Z = SY(KY)
               SX(KX) = W*SH11 + Z*SH12
               SY(KY) = W*SH21 + Z*SH22
               KX = KX + INCX
               KY = KY + INCY
            END DO
         ELSE IF (SFLAG.EQ.ZERO) THEN
            SH12 = SPARAM(4)
            SH21 = SPARAM(3)
            DO I = 1,N
               W = SX(KX)
               Z = SY(KY)
               SX(KX) = W + Z*SH12
               SY(KY) = W*SH21 + Z
               KX = KX + INCX
               KY = KY + INCY
            END DO
         ELSE
             SH11 = SPARAM(2)
             SH22 = SPARAM(5)
             DO I = 1,N
                W = SX(KX)
                Z = SY(KY)
                SX(KX) = W*SH11 + Z
                SY(KY) = -W + SH22*Z
                KX = KX + INCX
                KY = KY + INCY
            END DO
         END IF
      END IF
      RETURN
*
*     End of SROTM
*
      END