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- *DECK SROTM
- SUBROUTINE SROTM (N, SX, INCX, SY, INCY, SPARAM)
- C***BEGIN PROLOGUE SROTM
- C***PURPOSE Apply a modified Givens transformation.
- C***LIBRARY SLATEC (BLAS)
- C***CATEGORY D1A8
- C***TYPE SINGLE 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 SX single precision vector with N elements
- C INCX storage spacing between elements of SX
- C SY single precision vector with N elements
- C INCY storage spacing between elements of SY
- C SPARAM 5-element vector. SPARAM(1) is SFLAG described below.
- C Locations 2-5 of SPARAM contain elements of the
- C transformation matrix H described below.
- C
- C --Output--
- C SX rotated vector (unchanged if N .LE. 0)
- C SY rotated vector (unchanged if N .LE. 0)
- C
- C Apply the modified Givens transformation, H, to the 2 by N matrix
- C (SX**T)
- C (SY**T) , where **T indicates transpose. The elements of SX are
- C in SX(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 SY using LY and INCY.
- C
- 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 See SROTMG for a description of data storage 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 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 SROTM
- DIMENSION SX(*), SY(*), SPARAM(5)
- SAVE ZERO, TWO
- DATA ZERO, TWO /0.0E0, 2.0E0/
- C***FIRST EXECUTABLE STATEMENT SROTM
- SFLAG=SPARAM(1)
- IF (N.LE.0 .OR. (SFLAG+TWO.EQ.ZERO)) GO TO 140
- IF (.NOT.(INCX.EQ.INCY.AND. INCX .GT.0)) GO TO 70
- C
- NSTEPS=N*INCX
- IF (SFLAG) 50,10,30
- 10 CONTINUE
- SH12=SPARAM(4)
- SH21=SPARAM(3)
- DO 20 I = 1,NSTEPS,INCX
- W=SX(I)
- Z=SY(I)
- SX(I)=W+Z*SH12
- SY(I)=W*SH21+Z
- 20 CONTINUE
- GO TO 140
- 30 CONTINUE
- SH11=SPARAM(2)
- SH22=SPARAM(5)
- DO 40 I = 1,NSTEPS,INCX
- W=SX(I)
- Z=SY(I)
- SX(I)=W*SH11+Z
- SY(I)=-W+SH22*Z
- 40 CONTINUE
- GO TO 140
- 50 CONTINUE
- SH11=SPARAM(2)
- SH12=SPARAM(4)
- SH21=SPARAM(3)
- SH22=SPARAM(5)
- DO 60 I = 1,NSTEPS,INCX
- W=SX(I)
- Z=SY(I)
- SX(I)=W*SH11+Z*SH12
- SY(I)=W*SH21+Z*SH22
- 60 CONTINUE
- GO TO 140
- 70 CONTINUE
- KX=1
- KY=1
- IF (INCX .LT. 0) KX = 1+(1-N)*INCX
- IF (INCY .LT. 0) KY = 1+(1-N)*INCY
- C
- IF (SFLAG) 120,80,100
- 80 CONTINUE
- SH12=SPARAM(4)
- SH21=SPARAM(3)
- DO 90 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
- 90 CONTINUE
- GO TO 140
- 100 CONTINUE
- SH11=SPARAM(2)
- SH22=SPARAM(5)
- DO 110 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
- 110 CONTINUE
- GO TO 140
- 120 CONTINUE
- SH11=SPARAM(2)
- SH12=SPARAM(4)
- SH21=SPARAM(3)
- SH22=SPARAM(5)
- DO 130 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
- 130 CONTINUE
- 140 CONTINUE
- RETURN
- END
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