 LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ daxpy()

 subroutine daxpy ( integer N, double precision DA, double precision, dimension(*) DX, integer INCX, double precision, dimension(*) DY, integer INCY )

DAXPY

Purpose:
```    DAXPY constant times a vector plus a vector.
uses unrolled loops for increments equal to one.```
Parameters
 [in] N ``` N is INTEGER number of elements in input vector(s)``` [in] DA ``` DA is DOUBLE PRECISION On entry, DA specifies the scalar alpha.``` [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,out] DY ` DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )` [in] INCY ``` INCY is INTEGER storage spacing between elements of DY```
Further Details:
```     jack dongarra, linpack, 3/11/78.
modified 12/3/93, array(1) declarations changed to array(*)```

Definition at line 88 of file daxpy.f.

89 *
90 * -- Reference BLAS level1 routine --
91 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
92 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
93 *
94 * .. Scalar Arguments ..
95  DOUBLE PRECISION DA
96  INTEGER INCX,INCY,N
97 * ..
98 * .. Array Arguments ..
99  DOUBLE PRECISION DX(*),DY(*)
100 * ..
101 *
102 * =====================================================================
103 *
104 * .. Local Scalars ..
105  INTEGER I,IX,IY,M,MP1
106 * ..
107 * .. Intrinsic Functions ..
108  INTRINSIC mod
109 * ..
110  IF (n.LE.0) RETURN
111  IF (da.EQ.0.0d0) RETURN
112  IF (incx.EQ.1 .AND. incy.EQ.1) THEN
113 *
114 * code for both increments equal to 1
115 *
116 *
117 * clean-up loop
118 *
119  m = mod(n,4)
120  IF (m.NE.0) THEN
121  DO i = 1,m
122  dy(i) = dy(i) + da*dx(i)
123  END DO
124  END IF
125  IF (n.LT.4) RETURN
126  mp1 = m + 1
127  DO i = mp1,n,4
128  dy(i) = dy(i) + da*dx(i)
129  dy(i+1) = dy(i+1) + da*dx(i+1)
130  dy(i+2) = dy(i+2) + da*dx(i+2)
131  dy(i+3) = dy(i+3) + da*dx(i+3)
132  END DO
133  ELSE
134 *
135 * code for unequal increments or equal increments
136 * not equal to 1
137 *
138  ix = 1
139  iy = 1
140  IF (incx.LT.0) ix = (-n+1)*incx + 1
141  IF (incy.LT.0) iy = (-n+1)*incy + 1
142  DO i = 1,n
143  dy(iy) = dy(iy) + da*dx(ix)
144  ix = ix + incx
145  iy = iy + incy
146  END DO
147  END IF
148  RETURN
149 *
150 * End of DAXPY
151 *