Annotation of rpl/lapack/blas/idamax.f, revision 1.16
1.8 bertrand 1: *> \brief \b IDAMAX
2: *
3: * =========== DOCUMENTATION ===========
4: *
1.14 bertrand 5: * Online html documentation available at
6: * http://www.netlib.org/lapack/explore-html/
1.8 bertrand 7: *
8: * Definition:
9: * ===========
10: *
11: * INTEGER FUNCTION IDAMAX(N,DX,INCX)
1.14 bertrand 12: *
1.8 bertrand 13: * .. Scalar Arguments ..
14: * INTEGER INCX,N
15: * ..
16: * .. Array Arguments ..
17: * DOUBLE PRECISION DX(*)
18: * ..
1.14 bertrand 19: *
1.8 bertrand 20: *
21: *> \par Purpose:
22: * =============
23: *>
24: *> \verbatim
25: *>
1.12 bertrand 26: *> IDAMAX finds the index of the first element having maximum absolute value.
1.8 bertrand 27: *> \endverbatim
28: *
1.15 bertrand 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: *
1.8 bertrand 49: * Authors:
50: * ========
51: *
1.14 bertrand 52: *> \author Univ. of Tennessee
53: *> \author Univ. of California Berkeley
54: *> \author Univ. of Colorado Denver
55: *> \author NAG Ltd.
1.8 bertrand 56: *
1.15 bertrand 57: *> \date November 2017
1.8 bertrand 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: * =====================================================================
1.1 bertrand 72: INTEGER FUNCTION IDAMAX(N,DX,INCX)
1.8 bertrand 73: *
1.15 bertrand 74: * -- Reference BLAS level1 routine (version 3.8.0) --
1.8 bertrand 75: * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
76: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.15 bertrand 77: * November 2017
1.8 bertrand 78: *
1.1 bertrand 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
1.7 bertrand 99: IF (INCX.EQ.1) THEN
1.1 bertrand 100: *
1.7 bertrand 101: * code for increment equal to 1
1.1 bertrand 102: *
1.7 bertrand 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
1.1 bertrand 111: *
1.7 bertrand 112: * code for increment not equal to 1
1.1 bertrand 113: *
1.7 bertrand 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
1.1 bertrand 125: RETURN
126: END
CVSweb interface <joel.bertrand@systella.fr>