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 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 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 IDAMAX(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 DMAX
87: INTEGER I,IX
88: * ..
89: * .. Intrinsic Functions ..
90: INTRINSIC DABS
91: * ..
92: IDAMAX = 0
93: IF (N.LT.1 .OR. INCX.LE.0) RETURN
94: IDAMAX = 1
95: IF (N.EQ.1) RETURN
96: IF (INCX.EQ.1) THEN
97: *
98: * code for increment equal to 1
99: *
100: DMAX = DABS(DX(1))
101: DO I = 2,N
102: IF (DABS(DX(I)).GT.DMAX) THEN
103: IDAMAX = I
104: DMAX = DABS(DX(I))
105: END IF
106: END DO
107: ELSE
108: *
109: * code for increment not equal to 1
110: *
111: IX = 1
112: DMAX = DABS(DX(1))
113: IX = IX + INCX
114: DO I = 2,N
115: IF (DABS(DX(IX)).GT.DMAX) THEN
116: IDAMAX = I
117: DMAX = DABS(DX(IX))
118: END IF
119: IX = IX + INCX
120: END DO
121: END IF
122: RETURN
123: *
124: * End of IDAMAX
125: *
126: END
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