*DECK DASUM DOUBLE PRECISION FUNCTION DASUM (N, DX, INCX) C***BEGIN PROLOGUE DASUM C***PURPOSE Compute the sum of the magnitudes of the elements of a C vector. C***LIBRARY SLATEC (BLAS) C***CATEGORY D1A3A C***TYPE DOUBLE PRECISION (SASUM-S, DASUM-D, SCASUM-C) C***KEYWORDS BLAS, LINEAR ALGEBRA, SUM OF MAGNITUDES OF A 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 DX double precision vector with N elements C INCX storage spacing between elements of DX C C --Output-- C DASUM double precision result (zero if N .LE. 0) C C Returns sum of magnitudes of double precision DX. C DASUM = sum from 0 to N-1 of ABS(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 890531 Changed all specific intrinsics to generic. (WRB) 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 DASUM DOUBLE PRECISION DX(*) INTEGER I, INCX, IX, M, MP1, N C***FIRST EXECUTABLE STATEMENT DASUM DASUM = 0.0D0 IF (N .LE. 0) RETURN C 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 DASUM = DASUM + ABS(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 6. C 20 M = MOD(N,6) IF (M .EQ. 0) GOTO 40 DO 30 I = 1,M DASUM = DASUM + ABS(DX(I)) 30 CONTINUE IF (N .LT. 6) RETURN 40 MP1 = M + 1 DO 50 I = MP1,N,6 DASUM = DASUM + ABS(DX(I)) + ABS(DX(I+1)) + ABS(DX(I+2)) + 1 ABS(DX(I+3)) + ABS(DX(I+4)) + ABS(DX(I+5)) 50 CONTINUE RETURN END