*DECK DSCAL SUBROUTINE DSCAL (N, DA, DX, INCX) C***BEGIN PROLOGUE DSCAL C***PURPOSE Multiply a vector by a constant. C***LIBRARY SLATEC (BLAS) C***CATEGORY D1A6 C***TYPE DOUBLE PRECISION (SSCAL-S, DSCAL-D, CSCAL-C) C***KEYWORDS BLAS, LINEAR ALGEBRA, SCALE, 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 DA double precision scale factor C DX double precision vector with N elements C INCX storage spacing between elements of DX C C --Output-- C DX double precision result (unchanged if N.LE.0) C C Replace double precision DX by double precision DA*DX. C For I = 0 to N-1, replace DX(IX+I*INCX) with DA * DX(IX+I*INCX), C where IX = 1 if INCX .GE. 0, else IX = 1+(1-N)*INCX. 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 890831 Modified array declarations. (WRB) C 890831 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 900821 Modified to correct problem with a negative increment. C (WRB) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE DSCAL DOUBLE PRECISION DA, DX(*) INTEGER I, INCX, IX, M, MP1, N C***FIRST EXECUTABLE STATEMENT DSCAL IF (N .LE. 0) RETURN IF (INCX .EQ. 1) GOTO 20 C C Code for increment not equal to 1. C IX = 1 IF (INCX .LT. 0) IX = (-N+1)*INCX + 1 DO 10 I = 1,N DX(IX) = DA*DX(IX) IX = IX + INCX 10 CONTINUE RETURN C C Code for increment equal to 1. C C Clean-up loop so remaining vector length is a multiple of 5. C 20 M = MOD(N,5) IF (M .EQ. 0) GOTO 40 DO 30 I = 1,M DX(I) = DA*DX(I) 30 CONTINUE IF (N .LT. 5) RETURN 40 MP1 = M + 1 DO 50 I = MP1,N,5 DX(I) = DA*DX(I) DX(I+1) = DA*DX(I+1) DX(I+2) = DA*DX(I+2) DX(I+3) = DA*DX(I+3) DX(I+4) = DA*DX(I+4) 50 CONTINUE RETURN END