LAPACK  3.9.1
LAPACK: Linear Algebra PACKage

◆ ddot()

double precision function ddot ( integer  N,
double precision, dimension(*)  DX,
integer  INCX,
double precision, dimension(*)  DY,
integer  INCY 
)

DDOT

Purpose:
    DDOT forms the dot product of two vectors.
    uses unrolled loops for increments equal to one.
Parameters
[in]N
          N is INTEGER
         number of elements in input vector(s)
[in]DX
          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
[in]INCX
          INCX is INTEGER
         storage spacing between elements of DX
[in]DY
          DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
[in]INCY
          INCY is INTEGER
         storage spacing between elements of DY
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Further Details:
     jack dongarra, linpack, 3/11/78.
     modified 12/3/93, array(1) declarations changed to array(*)

Definition at line 81 of file ddot.f.

82 *
83 * -- Reference BLAS level1 routine --
84 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
85 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
86 *
87 * .. Scalar Arguments ..
88  INTEGER INCX,INCY,N
89 * ..
90 * .. Array Arguments ..
91  DOUBLE PRECISION DX(*),DY(*)
92 * ..
93 *
94 * =====================================================================
95 *
96 * .. Local Scalars ..
97  DOUBLE PRECISION DTEMP
98  INTEGER I,IX,IY,M,MP1
99 * ..
100 * .. Intrinsic Functions ..
101  INTRINSIC mod
102 * ..
103  ddot = 0.0d0
104  dtemp = 0.0d0
105  IF (n.LE.0) RETURN
106  IF (incx.EQ.1 .AND. incy.EQ.1) THEN
107 *
108 * code for both increments equal to 1
109 *
110 *
111 * clean-up loop
112 *
113  m = mod(n,5)
114  IF (m.NE.0) THEN
115  DO i = 1,m
116  dtemp = dtemp + dx(i)*dy(i)
117  END DO
118  IF (n.LT.5) THEN
119  ddot=dtemp
120  RETURN
121  END IF
122  END IF
123  mp1 = m + 1
124  DO i = mp1,n,5
125  dtemp = dtemp + dx(i)*dy(i) + dx(i+1)*dy(i+1) +
126  $ dx(i+2)*dy(i+2) + dx(i+3)*dy(i+3) + dx(i+4)*dy(i+4)
127  END DO
128  ELSE
129 *
130 * code for unequal increments or equal increments
131 * not equal to 1
132 *
133  ix = 1
134  iy = 1
135  IF (incx.LT.0) ix = (-n+1)*incx + 1
136  IF (incy.LT.0) iy = (-n+1)*incy + 1
137  DO i = 1,n
138  dtemp = dtemp + dx(ix)*dy(iy)
139  ix = ix + incx
140  iy = iy + incy
141  END DO
142  END IF
143  ddot = dtemp
144  RETURN
double precision function ddot(N, DX, INCX, DY, INCY)
DDOT
Definition: ddot.f:82
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