SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY) C***BEGIN PROLOGUE DAXPY C***DATE WRITTEN 791001 (YYMMDD) C***REVISION DATE 820801 (YYMMDD) C***CATEGORY NO. D1A7 C***KEYWORDS BLAS,DOUBLE PRECISION,LINEAR ALGEBRA,TRIAD,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***PURPOSE D.P computation y = a*x + y 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 DA double precision scalar multiplier C DX double precision vector with N elements C INCX storage spacing between elements of DX C DY double precision vector with N elements C INCY storage spacing between elements of DY C C --Output-- C DY double precision result (unchanged if N .LE. 0) C C Overwrite double precision DY with double precision DA*DX + DY. C For I = 0 to N-1, replace DY(LY+I*INCY) with DA*DX(LX+I*INCX) + C DY(LY+I*INCY), where LX = 1 if INCX .GE. 0, else LX = (-INCX)*N C and LY is defined in a similar way using INCY. C***REFERENCES LAWSON C.L., HANSON R.J., KINCAID D.R., KROGH F.T., C *BASIC LINEAR ALGEBRA SUBPROGRAMS FOR FORTRAN USAGE*, C ALGORITHM NO. 539, TRANSACTIONS ON MATHEMATICAL C SOFTWARE, VOLUME 5, NUMBER 3, SEPTEMBER 1979, 308-323 C***ROUTINES CALLED (NONE) C***END PROLOGUE DAXPY C DOUBLE PRECISION DX(1),DY(1),DA C***FIRST EXECUTABLE STATEMENT DAXPY IF(N.LE.0.OR.DA.EQ.0.D0) RETURN IF(INCX.EQ.INCY) IF(INCX-1) 5,20,60 5 CONTINUE C C CODE FOR NONEQUAL OR NONPOSITIVE INCREMENTS. C IX = 1 IY = 1 IF(INCX.LT.0)IX = (-N+1)*INCX + 1 IF(INCY.LT.0)IY = (-N+1)*INCY + 1 DO 10 I = 1,N DY(IY) = DY(IY) + DA*DX(IX) IX = IX + INCX IY = IY + INCY 10 CONTINUE RETURN C C CODE FOR BOTH INCREMENTS EQUAL TO 1 C C C CLEAN-UP LOOP SO REMAINING VECTOR LENGTH IS A MULTIPLE OF 4. C 20 M = MOD(N,4) IF( M .EQ. 0 ) GO TO 40 DO 30 I = 1,M DY(I) = DY(I) + DA*DX(I) 30 CONTINUE IF( N .LT. 4 ) RETURN 40 MP1 = M + 1 DO 50 I = MP1,N,4 DY(I) = DY(I) + DA*DX(I) DY(I + 1) = DY(I + 1) + DA*DX(I + 1) DY(I + 2) = DY(I + 2) + DA*DX(I + 2) DY(I + 3) = DY(I + 3) + DA*DX(I + 3) 50 CONTINUE RETURN C C CODE FOR EQUAL, POSITIVE, NONUNIT INCREMENTS. C 60 CONTINUE NS = N*INCX DO 70 I=1,NS,INCX DY(I) = DA*DX(I) + DY(I) 70 CONTINUE RETURN END