LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
isamax.f
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1 *> \brief \b ISAMAX
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * INTEGER FUNCTION ISAMAX(N,SX,INCX)
12 *
13 * .. Scalar Arguments ..
14 * INTEGER INCX,N
15 * ..
16 * .. Array Arguments ..
17 * REAL SX(*)
18 * ..
19 *
20 *
21 *> \par Purpose:
22 * =============
23 *>
24 *> \verbatim
25 *>
26 *> ISAMAX finds the index of the first element having maximum absolute value.
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] SX
39 *> \verbatim
40 *> SX is REAL 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 SX
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 aux_blas
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  INTEGER FUNCTION isamax(N,SX,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  REAL sx(*)
81 * ..
82 *
83 * =====================================================================
84 *
85 * .. Local Scalars ..
86  REAL smax
87  INTEGER i,ix
88 * ..
89 * .. Intrinsic Functions ..
90  INTRINSIC abs
91 * ..
92  isamax = 0
93  IF (n.LT.1 .OR. incx.LE.0) RETURN
94  isamax = 1
95  IF (n.EQ.1) RETURN
96  IF (incx.EQ.1) THEN
97 *
98 * code for increment equal to 1
99 *
100  smax = abs(sx(1))
101  DO i = 2,n
102  IF (abs(sx(i)).GT.smax) THEN
103  isamax = i
104  smax = abs(sx(i))
105  END IF
106  END DO
107  ELSE
108 *
109 * code for increment not equal to 1
110 *
111  ix = 1
112  smax = abs(sx(1))
113  ix = ix + incx
114  DO i = 2,n
115  IF (abs(sx(ix)).GT.smax) THEN
116  isamax = i
117  smax = abs(sx(ix))
118  END IF
119  ix = ix + incx
120  END DO
121  END IF
122  RETURN
123 *
124 * End of ISAMAX
125 *
126  END
integer function isamax(N, SX, INCX)
ISAMAX
Definition: isamax.f:71