summaryrefslogtreecommitdiff
path: root/SRC/izmax1.f
blob: 3f48c34896cd9b66f2997b8c1ffe011a5cb16f21 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
*> \brief \b IZMAX1 finds the index of the vector element whose real part has maximum absolute value.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*> \htmlonly
*> Download IZMAX1 + dependencies 
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/izmax1.f"> 
*> [TGZ]</a> 
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/izmax1.f"> 
*> [ZIP]</a> 
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/izmax1.f"> 
*> [TXT]</a>
*> \endhtmlonly 
*
*  Definition:
*  ===========
*
*       INTEGER          FUNCTION IZMAX1( N, CX, INCX )
* 
*       .. Scalar Arguments ..
*       INTEGER            INCX, N
*       ..
*       .. Array Arguments ..
*       COMPLEX*16         CX( * )
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> IZMAX1 finds the index of the element whose real part has maximum
*> absolute value.
*>
*> Based on IZAMAX from Level 1 BLAS.
*> The change is to use the 'genuine' absolute value.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of elements in the vector CX.
*> \endverbatim
*>
*> \param[in] CX
*> \verbatim
*>          CX is COMPLEX*16 array, dimension (N)
*>          The vector whose elements will be summed.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>          The spacing between successive values of CX.  INCX >= 1.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date September 2012
*
*> \ingroup complex16OTHERauxiliary
*
*> \par Contributors:
*  ==================
*>
*> Nick Higham for use with ZLACON.
*
*  =====================================================================
      INTEGER          FUNCTION IZMAX1( N, CX, INCX )
*
*  -- LAPACK auxiliary routine (version 3.4.2) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     September 2012
*
*     .. Scalar Arguments ..
      INTEGER            INCX, N
*     ..
*     .. Array Arguments ..
      COMPLEX*16         CX( * )
*     ..
*
* =====================================================================
*
*     .. Local Scalars ..
      INTEGER            I, IX
      DOUBLE PRECISION   SMAX
      COMPLEX*16         ZDUM
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          ABS
*     ..
*     .. Statement Functions ..
      DOUBLE PRECISION   CABS1
*     ..
*     .. Statement Function definitions ..
*
*     NEXT LINE IS THE ONLY MODIFICATION.
      CABS1( ZDUM ) = ABS( ZDUM )
*     ..
*     .. Executable Statements ..
*
      IZMAX1 = 0
      IF( N.LT.1 )
     $   RETURN
      IZMAX1 = 1
      IF( N.EQ.1 )
     $   RETURN
      IF( INCX.EQ.1 )
     $   GO TO 30
*
*     CODE FOR INCREMENT NOT EQUAL TO 1
*
      IX = 1
      SMAX = CABS1( CX( 1 ) )
      IX = IX + INCX
      DO 20 I = 2, N
         IF( CABS1( CX( IX ) ).LE.SMAX )
     $      GO TO 10
         IZMAX1 = I
         SMAX = CABS1( CX( IX ) )
   10    CONTINUE
         IX = IX + INCX
   20 CONTINUE
      RETURN
*
*     CODE FOR INCREMENT EQUAL TO 1
*
   30 CONTINUE
      SMAX = CABS1( CX( 1 ) )
      DO 40 I = 2, N
         IF( CABS1( CX( I ) ).LE.SMAX )
     $      GO TO 40
         IZMAX1 = I
         SMAX = CABS1( CX( I ) )
   40 CONTINUE
      RETURN
*
*     End of IZMAX1
*
      END