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*DECK SROT
SUBROUTINE SROT (N, SX, INCX, SY, INCY, SC, SS)
C***BEGIN PROLOGUE SROT
C***PURPOSE Apply a plane Givens rotation.
C***LIBRARY SLATEC (BLAS)
C***CATEGORY D1A8
C***TYPE SINGLE PRECISION (SROT-S, DROT-D, CSROT-C)
C***KEYWORDS BLAS, GIVENS ROTATION, GIVENS TRANSFORMATION,
C LINEAR ALGEBRA, PLANE 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 SC element of rotation matrix
C SS element of rotation matrix
C
C --Output--
C SX rotated vector SX (unchanged if N .LE. 0)
C SY rotated vector SY (unchanged if N .LE. 0)
C
C Multiply the 2 x 2 matrix ( SC SS) times the 2 x N matrix (SX**T)
C (-SS SC) (SY**T)
C where **T indicates transpose. The elements of SX are in
C 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***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 SROT
REAL SX, SY, SC, SS, ZERO, ONE, W, Z
DIMENSION SX(*), SY(*)
SAVE ZERO, ONE
DATA ZERO, ONE /0.0E0, 1.0E0/
C***FIRST EXECUTABLE STATEMENT SROT
IF (N .LE. 0 .OR. (SS .EQ. ZERO .AND. SC .EQ. ONE)) GO TO 40
IF (.NOT. (INCX .EQ. INCY .AND. INCX .GT. 0)) GO TO 20
C
C Code for equal and positive increments.
C
NSTEPS=INCX*N
DO 10 I = 1,NSTEPS,INCX
W=SX(I)
Z=SY(I)
SX(I)=SC*W+SS*Z
SY(I)=-SS*W+SC*Z
10 CONTINUE
GO TO 40
C
C Code for unequal or nonpositive increments.
C
20 CONTINUE
KX=1
KY=1
C
IF (INCX .LT. 0) KX = 1-(N-1)*INCX
IF (INCY .LT. 0) KY = 1-(N-1)*INCY
C
DO 30 I = 1,N
W=SX(KX)
Z=SY(KY)
SX(KX)=SC*W+SS*Z
SY(KY)=-SS*W+SC*Z
KX=KX+INCX
KY=KY+INCY
30 CONTINUE
40 CONTINUE
C
RETURN
END
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