LAPACK  3.8.0
LAPACK: Linear Algebra PACKage

◆ dscal()

subroutine dscal ( integer  N,
double precision  DA,
double precision, dimension(*)  DX,
integer  INCX 
)

DSCAL

Purpose:
    DSCAL scales a vector by a constant.
    uses unrolled loops for increment equal to 1.
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,out]DX
          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
[in]INCX
          INCX is INTEGER
         storage spacing between elements of DX
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2017
Further Details:
     jack dongarra, linpack, 3/11/78.
     modified 3/93 to return if incx .le. 0.
     modified 12/3/93, array(1) declarations changed to array(*)

Definition at line 81 of file dscal.f.

81 *
82 * -- Reference BLAS level1 routine (version 3.8.0) --
83 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
84 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
85 * November 2017
86 *
87 * .. Scalar Arguments ..
88  DOUBLE PRECISION da
89  INTEGER incx,n
90 * ..
91 * .. Array Arguments ..
92  DOUBLE PRECISION dx(*)
93 * ..
94 *
95 * =====================================================================
96 *
97 * .. Local Scalars ..
98  INTEGER i,m,mp1,nincx
99 * ..
100 * .. Intrinsic Functions ..
101  INTRINSIC mod
102 * ..
103  IF (n.LE.0 .OR. incx.LE.0) RETURN
104  IF (incx.EQ.1) THEN
105 *
106 * code for increment equal to 1
107 *
108 *
109 * clean-up loop
110 *
111  m = mod(n,5)
112  IF (m.NE.0) THEN
113  DO i = 1,m
114  dx(i) = da*dx(i)
115  END DO
116  IF (n.LT.5) RETURN
117  END IF
118  mp1 = m + 1
119  DO i = mp1,n,5
120  dx(i) = da*dx(i)
121  dx(i+1) = da*dx(i+1)
122  dx(i+2) = da*dx(i+2)
123  dx(i+3) = da*dx(i+3)
124  dx(i+4) = da*dx(i+4)
125  END DO
126  ELSE
127 *
128 * code for increment not equal to 1
129 *
130  nincx = n*incx
131  DO i = 1,nincx,incx
132  dx(i) = da*dx(i)
133  END DO
134  END IF
135  RETURN