LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
dasum.f
Go to the documentation of this file.
1 *> \brief \b DASUM
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * DOUBLE PRECISION FUNCTION DASUM(N,DX,INCX)
12 *
13 * .. Scalar Arguments ..
14 * INTEGER INCX,N
15 * ..
16 * .. Array Arguments ..
17 * DOUBLE PRECISION DX(*)
18 * ..
19 *
20 *
21 *> \par Purpose:
22 * =============
23 *>
24 *> \verbatim
25 *>
26 *> DASUM takes the sum of the absolute values.
27 *> \endverbatim
28 *
29 * Arguments:
30 * ==========
31 *
32 *> \param[in] N
33 *> \verbatim
34 *> N is INTEGER
35 *> number of elements in input vector(s)
36 *> \endverbatim
37 *>
38 *> \param[in] DX
39 *> \verbatim
40 *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
41 *> \endverbatim
42 *>
43 *> \param[in] INCX
44 *> \verbatim
45 *> INCX is INTEGER
46 *> storage spacing between elements of DX
47 *> \endverbatim
48 *
49 * Authors:
50 * ========
51 *
52 *> \author Univ. of Tennessee
53 *> \author Univ. of California Berkeley
54 *> \author Univ. of Colorado Denver
55 *> \author NAG Ltd.
56 *
57 *> \ingroup double_blas_level1
58 *
59 *> \par Further Details:
60 * =====================
61 *>
62 *> \verbatim
63 *>
64 *> jack dongarra, linpack, 3/11/78.
65 *> modified 3/93 to return if incx .le. 0.
66 *> modified 12/3/93, array(1) declarations changed to array(*)
67 *> \endverbatim
68 *>
69 * =====================================================================
70  DOUBLE PRECISION FUNCTION dasum(N,DX,INCX)
71 *
72 * -- Reference BLAS level1 routine --
73 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
74 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
75 *
76 * .. Scalar Arguments ..
77  INTEGER incx,n
78 * ..
79 * .. Array Arguments ..
80  DOUBLE PRECISION dx(*)
81 * ..
82 *
83 * =====================================================================
84 *
85 * .. Local Scalars ..
86  DOUBLE PRECISION dtemp
87  INTEGER i,m,mp1,nincx
88 * ..
89 * .. Intrinsic Functions ..
90  INTRINSIC dabs,mod
91 * ..
92  dasum = 0.0d0
93  dtemp = 0.0d0
94  IF (n.LE.0 .OR. incx.LE.0) RETURN
95  IF (incx.EQ.1) THEN
96 * code for increment equal to 1
97 *
98 *
99 * clean-up loop
100 *
101  m = mod(n,6)
102  IF (m.NE.0) THEN
103  DO i = 1,m
104  dtemp = dtemp + dabs(dx(i))
105  END DO
106  IF (n.LT.6) THEN
107  dasum = dtemp
108  RETURN
109  END IF
110  END IF
111  mp1 = m + 1
112  DO i = mp1,n,6
113  dtemp = dtemp + dabs(dx(i)) + dabs(dx(i+1)) +
114  $ dabs(dx(i+2)) + dabs(dx(i+3)) +
115  $ dabs(dx(i+4)) + dabs(dx(i+5))
116  END DO
117  ELSE
118 *
119 * code for increment not equal to 1
120 *
121  nincx = n*incx
122  DO i = 1,nincx,incx
123  dtemp = dtemp + dabs(dx(i))
124  END DO
125  END IF
126  dasum = dtemp
127  RETURN
128 *
129 * End of DASUM
130 *
131  END
double precision function dasum(N, DX, INCX)
DASUM
Definition: dasum.f:71