*DECK DCDOT
SUBROUTINE DCDOT (N, FM, CX, INCX, CY, INCY, DCR, DCI)
C***BEGIN PROLOGUE DCDOT
C***PURPOSE Compute the inner product of two vectors with extended
C precision accumulation and result.
C***LIBRARY SLATEC (BLAS)
C***CATEGORY D1A4
C***TYPE COMPLEX (DSDOT-D, DCDOT-C)
C***KEYWORDS BLAS, COMPLEX VECTORS, DOT PRODUCT, INNER PRODUCT,
C LINEAR ALGEBRA, VECTOR
C***AUTHOR (UNKNOWN)
C***DESCRIPTION
C
C Compute the dot product of 2 complex vectors, CX and CY, e.g.
C CX DOT CY, or, CXconjugate DOT CY. The real and imaginary
C parts of CX and CY are converted to double precision, the dot
C product accumulation is done in double precision and the output
C is given as 2 double precision numbers, corresponding to the real
C and imaginary part of the result.
C Input
C N: Number of complex components of CX and CY.
C FM: =+1.0 compute CX DOT CY.
C =-1.0 compute CXconjugate DOT CY.
C CX(N):
C CY(N): Complex arrays of length N.
C INCX:(Integer) Spacing of elements of CX to use
C INCY:(Integer) Spacing of elements of CY to use.
C Output
C DCR:(Double Precision) Real part of dot product.
C DCI:(Double Precision) Imaginary part of dot product.
C
C***REFERENCES (NONE)
C***ROUTINES CALLED (NONE)
C***REVISION HISTORY (YYMMDD)
C 790101 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***END PROLOGUE DCDOT
INTEGER I, INCX, INCY, KX, KY, N
COMPLEX CX(*), CY(*)
DOUBLE PRECISION DCR, DCI, DT1, DT2, DT3, DT4, FM
C***FIRST EXECUTABLE STATEMENT DCDOT
DCR = 0.0D0
DCI = 0.0D0
IF (N .LE. 0) GO TO 20
C
KX = 1
KY = 1
IF (INCX .LT. 0) KX = 1+(1-N)*INCX
IF (INCY .LT. 0) KY = 1+(1-N)*INCY
DO 10 I = 1,N
DT1 = DBLE(REAL(CX(KX)))
DT2 = DBLE(REAL(CY(KY)))
DT3 = DBLE(AIMAG(CX(KX)))
DT4 = DBLE(AIMAG(CY(KY)))
DCR = DCR+(DT1*DT2)-FM*(DT3*DT4)
DCI = DCI+(DT1*DT4)+FM*(DT3*DT2)
KX = KX+INCX
KY = KY+INCY
10 CONTINUE
20 RETURN
END