LAPACK 3.11.0 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 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