1: *> \brief \b IDAMAX
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 IDAMAX(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: *> IDAMAX 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] 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 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: *> \date November 2017
58: *
59: *> \ingroup aux_blas
60: *
61: *> \par Further Details:
62: * =====================
63: *>
64: *> \verbatim
65: *>
66: *> jack dongarra, linpack, 3/11/78.
67: *> modified 3/93 to return if incx .le. 0.
68: *> modified 12/3/93, array(1) declarations changed to array(*)
69: *> \endverbatim
70: *>
71: * =====================================================================
72: INTEGER FUNCTION IDAMAX(N,DX,INCX)
73: *
74: * -- Reference BLAS level1 routine (version 3.8.0) --
75: * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
76: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
77: * November 2017
78: *
79: * .. Scalar Arguments ..
80: INTEGER INCX,N
81: * ..
82: * .. Array Arguments ..
83: DOUBLE PRECISION DX(*)
84: * ..
85: *
86: * =====================================================================
87: *
88: * .. Local Scalars ..
89: DOUBLE PRECISION DMAX
90: INTEGER I,IX
91: * ..
92: * .. Intrinsic Functions ..
93: INTRINSIC DABS
94: * ..
95: IDAMAX = 0
96: IF (N.LT.1 .OR. INCX.LE.0) RETURN
97: IDAMAX = 1
98: IF (N.EQ.1) RETURN
99: IF (INCX.EQ.1) THEN
100: *
101: * code for increment equal to 1
102: *
103: DMAX = DABS(DX(1))
104: DO I = 2,N
105: IF (DABS(DX(I)).GT.DMAX) THEN
106: IDAMAX = I
107: DMAX = DABS(DX(I))
108: END IF
109: END DO
110: ELSE
111: *
112: * code for increment not equal to 1
113: *
114: IX = 1
115: DMAX = DABS(DX(1))
116: IX = IX + INCX
117: DO I = 2,N
118: IF (DABS(DX(IX)).GT.DMAX) THEN
119: IDAMAX = I
120: DMAX = DABS(DX(IX))
121: END IF
122: IX = IX + INCX
123: END DO
124: END IF
125: RETURN
126: END
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