*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