LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
izmax1.f
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00001 *> \brief \b IZMAX1
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download IZMAX1 + dependencies 
00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/izmax1.f"> 
00011 *> [TGZ]</a> 
00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/izmax1.f"> 
00013 *> [ZIP]</a> 
00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/izmax1.f"> 
00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       INTEGER          FUNCTION IZMAX1( N, CX, INCX )
00022 * 
00023 *       .. Scalar Arguments ..
00024 *       INTEGER            INCX, N
00025 *       ..
00026 *       .. Array Arguments ..
00027 *       COMPLEX*16         CX( * )
00028 *       ..
00029 *  
00030 *
00031 *> \par Purpose:
00032 *  =============
00033 *>
00034 *> \verbatim
00035 *>
00036 *> IZMAX1 finds the index of the element whose real part has maximum
00037 *> absolute value.
00038 *>
00039 *> Based on IZAMAX from Level 1 BLAS.
00040 *> The change is to use the 'genuine' absolute value.
00041 *> \endverbatim
00042 *
00043 *  Arguments:
00044 *  ==========
00045 *
00046 *> \param[in] N
00047 *> \verbatim
00048 *>          N is INTEGER
00049 *>          The number of elements in the vector CX.
00050 *> \endverbatim
00051 *>
00052 *> \param[in] CX
00053 *> \verbatim
00054 *>          CX is COMPLEX*16 array, dimension (N)
00055 *>          The vector whose elements will be summed.
00056 *> \endverbatim
00057 *>
00058 *> \param[in] INCX
00059 *> \verbatim
00060 *>          INCX is INTEGER
00061 *>          The spacing between successive values of CX.  INCX >= 1.
00062 *> \endverbatim
00063 *
00064 *  Authors:
00065 *  ========
00066 *
00067 *> \author Univ. of Tennessee 
00068 *> \author Univ. of California Berkeley 
00069 *> \author Univ. of Colorado Denver 
00070 *> \author NAG Ltd. 
00071 *
00072 *> \date November 2011
00073 *
00074 *> \ingroup complex16OTHERauxiliary
00075 *
00076 *> \par Contributors:
00077 *  ==================
00078 *>
00079 *> Nick Higham for use with ZLACON.
00080 *
00081 *  =====================================================================
00082       INTEGER          FUNCTION IZMAX1( N, CX, INCX )
00083 *
00084 *  -- LAPACK auxiliary routine (version 3.4.0) --
00085 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00086 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00087 *     November 2011
00088 *
00089 *     .. Scalar Arguments ..
00090       INTEGER            INCX, N
00091 *     ..
00092 *     .. Array Arguments ..
00093       COMPLEX*16         CX( * )
00094 *     ..
00095 *
00096 * =====================================================================
00097 *
00098 *     .. Local Scalars ..
00099       INTEGER            I, IX
00100       DOUBLE PRECISION   SMAX
00101       COMPLEX*16         ZDUM
00102 *     ..
00103 *     .. Intrinsic Functions ..
00104       INTRINSIC          ABS
00105 *     ..
00106 *     .. Statement Functions ..
00107       DOUBLE PRECISION   CABS1
00108 *     ..
00109 *     .. Statement Function definitions ..
00110 *
00111 *     NEXT LINE IS THE ONLY MODIFICATION.
00112       CABS1( ZDUM ) = ABS( ZDUM )
00113 *     ..
00114 *     .. Executable Statements ..
00115 *
00116       IZMAX1 = 0
00117       IF( N.LT.1 )
00118      $   RETURN
00119       IZMAX1 = 1
00120       IF( N.EQ.1 )
00121      $   RETURN
00122       IF( INCX.EQ.1 )
00123      $   GO TO 30
00124 *
00125 *     CODE FOR INCREMENT NOT EQUAL TO 1
00126 *
00127       IX = 1
00128       SMAX = CABS1( CX( 1 ) )
00129       IX = IX + INCX
00130       DO 20 I = 2, N
00131          IF( CABS1( CX( IX ) ).LE.SMAX )
00132      $      GO TO 10
00133          IZMAX1 = I
00134          SMAX = CABS1( CX( IX ) )
00135    10    CONTINUE
00136          IX = IX + INCX
00137    20 CONTINUE
00138       RETURN
00139 *
00140 *     CODE FOR INCREMENT EQUAL TO 1
00141 *
00142    30 CONTINUE
00143       SMAX = CABS1( CX( 1 ) )
00144       DO 40 I = 2, N
00145          IF( CABS1( CX( I ) ).LE.SMAX )
00146      $      GO TO 40
00147          IZMAX1 = I
00148          SMAX = CABS1( CX( I ) )
00149    40 CONTINUE
00150       RETURN
00151 *
00152 *     End of IZMAX1
00153 *
00154       END
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