LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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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 element having max. absolute value.
27 *> \endverbatim
28 *
29 * Authors:
30 * ========
31 *
32 *> \author Univ. of Tennessee
33 *> \author Univ. of California Berkeley
34 *> \author Univ. of Colorado Denver
35 *> \author NAG Ltd.
36 *
37 *> \date November 2011
38 *
39 *> \ingroup aux_blas
40 *
41 *> \par Further Details:
42 * =====================
43 *>
44 *> \verbatim
45 *>
46 *> jack dongarra, linpack, 3/11/78.
47 *> modified 3/93 to return if incx .le. 0.
48 *> modified 12/3/93, array(1) declarations changed to array(*)
49 *> \endverbatim
50 *>
51 * =====================================================================
52  INTEGER FUNCTION isamax(N,SX,INCX)
53 *
54 * -- Reference BLAS level1 routine (version 3.4.0) --
55 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
56 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
57 * November 2011
58 *
59 * .. Scalar Arguments ..
60  INTEGER incx,n
61 * ..
62 * .. Array Arguments ..
63  REAL sx(*)
64 * ..
65 *
66 * =====================================================================
67 *
68 * .. Local Scalars ..
69  REAL smax
70  INTEGER i,ix
71 * ..
72 * .. Intrinsic Functions ..
73  INTRINSIC abs
74 * ..
75  isamax = 0
76  IF (n.LT.1 .OR. incx.LE.0) return
77  isamax = 1
78  IF (n.EQ.1) return
79  IF (incx.EQ.1) THEN
80 *
81 * code for increment equal to 1
82 *
83  smax = abs(sx(1))
84  DO i = 2,n
85  IF (abs(sx(i)).GT.smax) THEN
86  isamax = i
87  smax = abs(sx(i))
88  END IF
89  END DO
90  ELSE
91 *
92 * code for increment not equal to 1
93 *
94  ix = 1
95  smax = abs(sx(1))
96  ix = ix + incx
97  DO i = 2,n
98  IF (abs(sx(ix)).GT.smax) THEN
99  isamax = i
100  smax = abs(sx(ix))
101  END IF
102  ix = ix + incx
103  END DO
104  END IF
105  return
106  END